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#### Physics 9th Edition Cutnellī¨- Test Bank

Import Settings:Base Settings: Brownstone DefaultInformation Field: DifficultyInformation Field: SectionDefHighest Answer Letter: EMultiple Keywords in Same Paragraph: No Chapter: Chapter 6 Multiple Choice

- In which one of the following situations is zero net work done?
- A) A ball rolls down an inclined plane.
- B) A physics student stretches a spring.
- C) A projectile falls toward the surface of Earth.
- D) A box is pulled across a rough floor at constant velocity.
- E) A child pulls a toy across a rough surface causing it to accelerate.

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- Complete the following statement: Work may be expressed using all of the following units
*except* - A) N Ã
- B)
- C)
- D) ft Ã
- E)

Ans:Â EDifficulty:Â EasySectionDef:Â Section 6-1 and 6-2

- A concrete block is pulled 7.0 m across a frictionless surface by means of a rope. The tension in the rope is 40 N; and the net work done on the block is 247 J.Â What angle does the rope make with the horizontal?
- A) 28Â°
- B) 41Â°
- C) 47Â°
- D) 62Â°
- E) 88Â°

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- Mike is cutting the grass using a human-powered lawn mower. He pushes the mower with a force of 45 N directed at an angle of 41Â° below the horizontal direction.Â Calculate the work that Mike does on the mower each time he pushes it 9.1 m across the yard.
- A) 510 J
- B) 260 J
- C) 410 J
- D) 360 J
- E) 310 J

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- A 5.00-kg block of ice is sliding across a frozen pond at 2.00 m/s. A 7.60-N force is applied in the direction of motion.Â After the ice block slides 15.0 m, the force is removed.Â The work done by the applied force is
- A) â114 J.
- B) +114 J.
- C) â735 J.
- D) +735 J.
- E) +19.7 J.

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- A force with a magnitude of 25 N and directed at an angle of 37Â° above the horizontal is used to move a 10-kg crate along a horizontal surface at constant velocity. How much work is done by this force in moving the crate a distance of 15 m?
- A) zero joules
- B) 7 J
- C) 40 J
- D) 98 J
- E) 300 J

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- A constant force of 25 N is applied as shown to a block which undergoes a displacement of 7.5 m to the right along a frictionless surface while the force acts. What is the work done by the force?
- A) zero joules
- B) +94 J
- C) â94 J
- D) +160 J
- E) â160 J

Ans:Â CDifficulty:Â HardSectionDef:Â Section 6-1 and 6-2

- A 1.0-kg ball on the end of a string is whirled at a constant speed of 2.0 m/s in a horizontal circle of radius 1.5 m. What is the work done by the centripetal force during one revolution?
- A) zero joules
- B) 7 J
- C) 0 J
- D) 25 J
- E) 33 J

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- Julie carries an 8.0-kg suitcase as she walks 18 m along a horizontal walkway to her hotel room at a constant speed of 1.5 m/s. How much work does Julie do in carrying her suitcase?
- A) zero joules
- B) 40 J
- C) 200 J
- D) 300 J
- E) 2000 J

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- Which one of the following situations is an example of an object with a non-zero kinetic energy?
- A) a drum of diesel fuel on a parked truck
- B) a stationary pendulum
- C) a satellite in geosynchronous orbit
- D) a car parked at the top of a hill
- E) a boulder resting at the bottom of a cliff

Ans:Â CDifficulty:Â EasySectionDef:Â Section 6-1 and 6-2

- Which one of the following statements concerning kinetic energy is true?
- A) Kinetic energy can be measured in watts.
- B) Kinetic energy is always equal to the potential energy.
- C) Kinetic energy is always positive.
- D) Kinetic energy is a quantitative measure of inertia.
- E) Kinetic energy is directly proportional to velocity.

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- Which one of the following has the largest kinetic energy?
- A) a raindrop falling
- B) a woman swimming
- C) a jet airplane flying at its maximum speed
- D) the earth moving in its orbit around the sun
- E) the space shuttle orbiting the Earth

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- In which one of the following situations will there be an
*increase*in kinetic energy? - A) A projectile approaches its maximum height.
- B) A ball starts from rest and freely rolls downhill.
- C) A box is pulled across a rough floor at constant speed.
- D) A satellite travels in a circular orbit around the earth at fixed altitude.
- E) A stone at the end of a string is whirled in a horizontal circle at constant speed.

Ans:Â BDifficulty:Â EasySectionDef:Â Section 6-1 and 6-2

- An experimental 1500-kg car travels at a constant speed of 22 m/s around a circular test track that is 80 m across. What is the kinetic energy of the car?
- A) zero joules
- B) 6 Ã 10
^{5}J - C) 3 Ã 10
^{4}J - D) 6 Ã 10
^{4}J - E) 2 Ã 10
^{5}J

Ans:Â BDifficulty:Â EasySectionDef:Â Section 6-1 and 6-2

- The kinetic energy of a car is 8 Ã 10
^{6}J as it travels along a horizontal road. How much work is required to stop the car in 10 s? - A) zero joules
- B) 8 Ã 10
^{4}J - C) 8 Ã 10
^{5}J - D) 8 Ã 10
^{6}J - E) 8 Ã 10
^{7}J

Ans:Â DDifficulty:Â EasySectionDef:Â Section 6-1 and 6-2

- How much energy is dissipated in braking a 1200-kg car to a stop from an initial speed of 30 m/s?
- A) 24 000 J
- B) 280 000 J
- C) 540 000 J
- D) 820 000 J
- E) 12 000 J

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- The kinetic energy of an 1800-kg truck is 7.2 Ã 10
^{5}J. What is the speed of the truck? - A) 25 m/s
- B) 33 m/s
- C) 28 m/s
- D) 17 m/s
- E) 21 m/s

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- A 10.0-g bullet traveling horizontally at 755 m/s strikes a stationary target and stops after penetrating 14.5 cm into the target. What is the average force of the target on the bullet?
- A) 97 Ã 10
^{4}N - B) 07 Ã 10
^{5}N - C) 26 Ã 10
^{3}N - D) 13 Ã 10
^{4}N - E) 93 Ã 10
^{4}N

Ans:Â ADifficulty:Â HardSectionDef:Â Section 6-1 and 6-2

- A car is traveling at 7.0 m/s when the driver applies the brakes. The car moves 1.5 m before it comes to a complete stop.Â If the car had been moving at 14 m/s, how far would it have continued to move after the brakes were applied?Â Assume the braking force in both cases is constant and the same.
- A) 5 m
- B) 0 m
- C) 5 m
- D) 0 m
- E) 5 m

Ans:Â DDifficulty:Â HardSectionDef:Â Section 6-1 and 6-2

- Use the work-energy theorem to find the force required to accelerate an electron (
*m*= 9.11 Ã 10^{â31}kg) moving along the*x*axis from 4.00 Ã 10^{6}m/s to 1.60 Ã 10^{7}m/s in a distance of 0.0125 m. - A) 75 Ã 10
^{â15}N - B) 47 Ã 10
^{â22}N - C) 20 Ã 10
^{â17}N - D) 64 Ã 10
^{â14}N - E) 56 Ã 10
^{â19}N

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-1 and 6-2

- In which one of the following systems is there a
*decrease*in gravitational potential energy? - A) a boy stretches a horizontal spring
- B) a girl jumps down from a bed
- C) a crate rests at the bottom of an inclined plane
- D) a car ascends a steep hill
- E) water is forced upward through a pipe

Ans:Â BDifficulty:Â EasySectionDef:Â Section 6-3 and 6-4

- An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force.Â Which one of the following statements is true?
- A) The magnitude of the work done by the tension force is larger than that done by the gravitational force.
- B) The magnitude of the work done by the gravitational force is larger than that done by the tension force.
- C) The work done by the tension force is zero joules.
- D) The work done by the gravitational force is zero joules.
- E) The net work done by the two forces is zero joules.

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- During the construction of a high rise building, 40-kg block is vertically lifted 20 meters from the surface of the earth. To one significant figure, what is the change in the gravitational potential energy of the block?
- A) +800 J
- B) â800 J
- C) +8000 J
- D) â8000 J
- E) zero joules

Ans:Â CDifficulty:Â EasySectionDef:Â Section 6-3 and 6-4

- A 1500-kg elevator moves upward with constant speed through a vertical distance of 25 m. How much work was done by the tension in the elevator cable?
- A) 990 J
- B) 8100 J
- C) 140 000 J
- D) 370 000 J
- E) 430 000 J

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- Larry’s gravitational potential energy is 1870 J as he sits 2.20 m above the ground in a sky diving airplane before it takes off. What is Larry’s gravitational potential energy when be begins to jump from the airplane at an altitude of 923 m?
- A) 85 Ã 10
^{5}J - B) 87 Ã 10
^{3}J - C) 29 Ã 10
^{4}J - D) 36 Ã 10
^{2}J - E) 22 Ã 10
^{6}J

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- Two balls of equal size are dropped from the same height from the roof of a building. One ball has twice the mass of the other.Â When the balls reach the ground, how do the kinetic energies of the two balls compare?
- A) The lighter one has one fourth as much kinetic energy as the other does.
- B) The lighter one has one half as much kinetic energy as the other does.
- C) The lighter one has the same kinetic energy as the other does.
- D) The lighter one has twice as much kinetic energy as the other does.
- E) The lighter one has four times as much kinetic energy as the other does.

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- A 12-kg crate is pushed up an incline from point A to point B as shown in the figure. What is the change in the gravitational potential energy of the crate?
- A) +590 J
- B) â590 J
- C) +1200 J
- D) â1200 J
- E) This cannot be determined without knowing the angle of the incline.

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- A woman stands on the edge of a cliff and throws a stone
*vertically downward*with an initial speed of 10 m/s. The instant before the stone hits the ground below, it has 450 J of kinetic energy.Â If she were to throw the stone*horizontally outward*from the cliff with the same initial speed of 10 m/s, how much kinetic energy would it have just before it hits the ground? - A) 50 J
- B) 100 J
- C) 450 J
- D) 800 J
- E) 950 J

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- A donkey pulls a crate up a rough, inclined plane at constant speed. Which one of the following statements concerning this situation is false?
- A) The gravitational potential energy of the crate is increasing.
- B) The net work done by all the forces acting on the crate is zero joules.
- C) The work done on the crate by the normal force of the plane is zero joules.
- D) The donkey does “positive” work in pulling the crate up the incline.
- E) The work done on the object by gravity is zero joules.

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- A block is dropped from a high tower and is falling freely under the influence of gravity. Which one of the following statements is true concerning this situation?Â Neglect air resistance.
- A) As the block falls, the net work done by all of the forces acting on the block is zero joules.
- B) The kinetic energy increases by equal amounts over equal distances.
- C) The kinetic energy of the block increases by equal amounts in equal times.
- D) The potential energy of the block decreases by equal amounts in equal times.
- E) The total energy of the block increases by equal amounts over equal distances.

Ans:Â BDifficulty:Â HardSectionDef:Â Section 6-3 and 6-4

- A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises?Â Neglect air resistance.
- A) The total energy of the rock increases.
- B) The kinetic energy increases and the potential energy decreases.
- C) Both the potential energy and the total energy of the rock increase.
- D) The kinetic energy decreases and the potential energy increases.
- E) Both the kinetic energy and the potential energy of the rock remain the same.

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- Complete the following statement: A force that acts on an object is said to be
*conservative*if - A) it obeys Newton’s laws of motion.
- B) it results in a change in the object’s kinetic energy.
- C) it always acts in the direction of motion of the object.
- D) the work it does on the object is independent of the path of the motion.
- E) the work it does on the object is equal to the increase in the object’s kinetic energy.

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-3 and 6-4

- Which one of the following choices is an example of a conservative force?
- A) tension
- B) normal force
- C) static frictional force
- D) motor propulsion force
- E) elastic spring force

Ans:Â EDifficulty:Â EasySectionDef:Â Section 6-3 and 6-4

- Which one of the following choices is an example of a non-conservative force?
- A) gravitational force
- B) electrical force
- C) kinetic frictional force
- D) elastic spring force

Ans:Â CDifficulty: Â EasySectionDef:Â Section 6-3 and 6-4

- A helicopter (
*m*= 3250 kg) is cruising at a speed of 56.9 m/s at an altitude of 185 m. What is the total mechanical energy of the helicopter? - A) 91 Ã 10
^{7}J - B) 26 Ã 10
^{7}J - C) 27 Ã 10
^{8}J - D) 91 Ã 10
^{7}J - E) 12 Ã 10
^{8}J

Ans:Â EDifficulty:Â EasySectionDef:Â Section 6-5

- A pebble rolls off the roof of Science Hall and falls vertically. Just before it reaches the ground, the pebble’s speed is 17 m/s.Â Neglect air resistance and determine the height of Science Hall.
- A) 42 m
- B) 33 m
- C) 26 m
- D) 21 m
- E) 15 m

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-5 Reference:Â Ref 6-1 A 2.0-kg projectile is fired with initial velocity components *v*_{ox} = 30 m/s and *v*_{oy} = 40 m/s from a point on the earth’s surface.Â Neglect any effects due to air resistance.

- What is the kinetic energy of the projectile when it reaches the highest point in its trajectory?
- A) zero joules
- B) 900 J
- C) 1600 J
- D) 2500 J
- E) 4900 J

Ans:Â BRefer To:Â Ref 6-1Difficulty:Â MediumSectionDef:Â Section 6-5

- How much work was done in firing the projectile?
- A) 900 J
- B) 1600 J
- C) 2500 J
- D) 4900 J
- E) 9800 J

Ans:Â CRefer To:Â Ref 6-1Difficulty:Â HardSectionDef:Â Section 6-5

- Two boxes are connected to each other as shown. The system is released from rest and the 1.00-kg box falls through a distance of 1.00 m.Â The surface of the table is frictionless.Â What is the kinetic energy of box B just before it reaches the floor?
- A) 45 J
- B) 90 J
- C) 80 J
- D) 4 J
- E) 2 J

Ans:Â ADifficulty:Â HardSectionDef:Â Section 6-5

- A roller-coaster car is moving at 20 m/s along a straight horizontal track. What will its speed be after climbing the 15-m hill shown in the figure, if friction is ignored?
- A) 17 m/s
- B) 7 m/s
- C) 5 m/s
- D) 10 m/s
- E) 14 m/s

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-5

- A 3.0-kg cylinder falls vertically from rest in a very tall, evacuated tube near the surface of the earth. What is its speed after the cylinder has fallen 6.0 m?
- A) 0 m/s
- B) 11 m/s
- C) 13 m/s
- D) 120 m/s
- E) 26 m/s

Ans:Â BDifficulty:Â EasySectionDef:Â Section 6-5

- A bicyclist is traveling at a speed of 20.0 m/s as he approaches the bottom of a hill. He decides to coast up the hill and stops upon reaching the top.Â Neglecting friction, determine the vertical height of the hill.
- A) 5 m
- B) 70 m
- C) 2 m
- D) 8 m
- E) 4 m

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-5

- A skier leaves the top of a slope with an initial speed of 5.0 m/s. Her speed at the bottom of the slope is 13 m/s.Â What is the height of the slope?
- A) 1 m
- B) 6 m
- C) 4 m
- D) 3 m
- E) 11 m

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-5

- A roller coaster starts from rest at the top of an 18-m hill as shown. The car travels to the bottom of the hill and continues up the next hill that is 10.0 m high.

How fast is the car moving at the top of the 10.0-m hill, if friction is ignored?

- A) 4 m/s
- B) 1 m/s
- C) 13 m/s
- D) 18 m/s
- E) 27 m/s

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 6-5

- An engineer is asked to design a playground slide such that the speed a child reaches at the bottom does not exceed 6.0 m/s.

Determine the maximum height that the slide can be.

- A) 8 m
- B) 9 m
- C) 2 m
- D) 5 m
- E) 4 m

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 6-5

- A care package is dropped from rest from a helicopter hovering 25 m above the ground.What is the speed of the package just before it reaches the ground? Neglect air resistance.
- A) 22 m/s
- B) 16 m/s
- C) 12 m/s
- D) 0 m/s
- E) 0 m/s

Ans:Â ADifficulty:Â EasySectionDef:Â Section 6-5 Reference:Â Ref 6-2 A block of mass *m* is released from rest at a height *R* above a horizontal surface.Â The acceleration due to gravity is *g*.Â The block slides along the inside of a frictionless circular hoop of radius *R*.

- Which one of the following expressions gives the speed of the mass at the bottom of the hoop?
- A) zero m/s
^{2} - B)
*v*=*mgR* - C)
- D)
- E)
*v*^{2}= 2*gR*

Ans:Â ERefer To:Â Ref 6-2Difficulty:Â MediumSectionDef:Â Section 6-5

- What is the magnitude of the normal force exerted on the block by the hoop when the block reaches the bottom of the hoop?
- A) zero newtons
- B)
*mg*^{2}/*R* - C)
*mg* - D) 2
*mg* - E) 3
*mg*

Ans:Â ERefer To:Â Ref 6-2Difficulty:Â HardSectionDef:Â Section 6-5

- A physics student shoves a 0.50-kg block from the bottom of a frictionless 30.0Â° inclined plane. The student performs 4.0 J of work and the block slides a distance
*s*along the incline before it stops.Â Determine the value of*s*. - A) 0 cm
- B) 16 cm
- C) 82 cm
- D) 160 cm
- E) 330 cm

Ans:Â DDifficulty:Â HardSectionDef:Â Section 6-6

- The initial velocity of a 4.0-kg box is 11 m/s, due west. After the box slides 4.0 m horizontally, its speed is 1.5 m/s.Â Determine the magnitude and the direction of the non-conservative force acting on the box as it slides.
- A) 42 N, due west
- B) 120 N, due east
- C) 31 N, due east
- D) 59 N, due east
- E) 83 N, due west

Ans:Â DDifficulty:Â HardSectionDef:Â Section 6-6

- An automobile approaches a barrier at a speed of 20 m/s along a level road. The driver locks the brakes at a distance of 50 m from the barrier.Â What minimum coefficient of kinetic friction is required to stop the automobile before it hits the barrier?
- A) 4
- B) 5
- C) 6
- D) 7
- E) 8

Ans:Â ADifficulty:Â HardSectionDef:Â Section 6-6 Reference:Â Ref 6-3 A 9.0-kg box of oranges slides from rest down a frictionless incline from a height of 5.0 m.Â A constant frictional force, introduced at point **A**, brings the block to rest at point **B**, 19 m to the right of point **A**.

- What is the speed of the box just before it reaches point A?
- A) 98 m/s
- B) 21 m/s
- C) 9 m/s
- D) 7 m/s
- E) 4 m/s

Ans:Â CRefer To:Â Ref 6-3Difficulty:Â MediumSectionDef:Â Section 6-6

- What is the coefficient of kinetic friction, m
_{k}, of the surface from A to B? - A) 11
- B) 26
- C) 33
- D) 47
- E) 52

Ans:Â BRefer To:Â Ref 6-3Difficulty:Â HardSectionDef:Â Section 6-6

- The kinetic energy of a car is 8 Ã 10
^{6}J as it travels along a horizontal road. How much power is required to stop the car in 10 s? - A) zero watts
- B) 8 Ã 10
^{4}W - C) 8 Ã 10
^{5}W - D) 8 Ã 10
^{6}W - E) 8 Ã 10
^{7}W

Ans:Â CDifficulty:Â EasySectionDef:Â Section 6-7

- A 51-kg woman runs up a flight of stairs in 5.0 s. Her net upward displacement is 5.0 m.Â Approximately, what average power did the woman exert while she was running?
- A) 0 kW
- B) 0 kW
- C) 75 kW
- D) 50 kW
- E) 25 kW

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-7

- What power is needed to lift a 49-kg person a vertical distance of 5.0 m in 20.0 s?
- A) 5 W
- B) 25 W
- C) 60 W
- D) 120 W
- E) 210 W

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 6-7

- An escalator is 30.0 meters long and slants at 30.0Â° relative to the horizontal. If it moves at 1.00 m/s, at what rate does it do work in lifting a 50.0-kg woman from the bottom to the top of the escalator?
- A) 3 W
- B) 0 W
- C) 245 W
- D) 292 W
- E) 495 W

Ans:Â CDifficulty:Â HardSectionDef:Â Section 6-7

- How much power is needed to lift a 75-kg student vertically upward at a constant speed of 0.33 m/s?
- A) 5 W
- B) 25 W
- C) 115 W
- D) 230 W
- E) 243 W

Ans:Â EDifficulty:Â HardSectionDef:Â Section 6-7

- A warehouse worker uses a forklift to raise a crate of pickles on a platform to a height 2.75 m above the floor. The combined mass of the platform and the crate is 207 kg.Â If the power expended by the forklift is 1440 W, how long does it take to lift the crate?
- A) 2 s
- B) 81 s
- C) 87 s
- D) 6 s
- E) 86 s

Ans:Â CDifficulty:Â HardSectionDef:Â Section 6-7

- A dam is used to block the passage of a river and to generate electricity. Approximately 5.73 Â´ 10
^{4}kg of water fall each second through a height of 19.6 m.Â If 85 % of the gravitational potential energy of the water were converted to electrical energy, how much power would be generated? - A) 36 Â´ 10
^{6}W - B) 52 Â´ 10
^{7}W - C) 08 Â´ 10
^{7}W - D) 35 Â´ 10
^{8}W - E) 4.68 Â´ 10
^{6}W

Ans:Â ADifficulty:Â HardSectionDef:Â Section 6-7

- The amount of energy needed to power a 0.10-kW bulb for one minute would be just sufficient to lift a 1.0-kg object through a vertical distance of
- A) 12 m
- B) 75 m
- C) 100 m
- D) 120 m
- E) 610 m

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 6-7

- The graph shows the force component along the displacement as a function of the magnitude of the displacement. Determine the work done by the force during the interval from 2 to 10 m.
- A) 140 J
- B) 190 J
- C) 270 J
- D) 450 J
- E) 560 J

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 6-9

- The force component acting on an object along the displacement varies with the displacement
*s*as shown in the graph. Determine the work done on the object as it travels from*s*= 0.0 to 12 m. - A) 48 J
- B) 66 J
- C) 72 J
- D) 57 J
- E) 81 J

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 6-9

- Which one of the following is
*not*a unit of energy? - A) foot Ã pound
- B) kilowatt Ã hour
- C) newton Ã meter
- D) watt
- E) joule

Ans:Â DDifficulty:Â EasySectionDef:Â Additional Problems Reference:Â Ref 6-4 A 0.50-kg ball on the end of a rope is moving in a vertical circle of radius 3.0 m near the surface of the Earth where the acceleration due to gravity, *g*, is 9.8 m/s^{2}.Â Point **A** is at the top of the circle; **C** is at the bottom.Â Points **B** and **D** are exactly halfway between **A** and **C**.

- Which one of the following statements concerning the tension in the rope is true?
- A) The tension is smallest at
**A**. - B) The tension is smallest at
**C**. - C) The tension is smallest at both
**B**and**D**. - D) The tension is the same at
**A**and**C**. - E) The tension is the same at
**A**,**B**,**C**, and**D**.

Ans:Â ARefer To:Â Ref 6-4Difficulty:Â EasySectionDef:Â Additional Problems

- The ball moves on the circle from
**A**to**C**under the influence of gravity alone. If the kinetic energy of the ball is 35 J at**A**, what is its kinetic energy at**C**? - A) zero joules
- B) 29 J
- C) 35 J
- D) 44 J
- E) 64 J

Ans:Â ERefer To:Â Ref 6-4Difficulty:Â MediumSectionDef:Â Additional Problems

- A motorist driving a 1000-kg car wishes to increase her speed from 20 m/s to 30 m/s in 5 s. Determine the horsepower required to accomplish this increase.Â Neglect friction.
- A) 20 hp
- B) 30 hp
- C) 70 hp
- D) 80 hp
- E) 90 hp

Ans:Â CDifficulty:Â HardSectionDef:Â Additional Problems

- A top fuel dragster with a mass of 500.0 kg starts from rest and completes a quarter mile (402 m) race in a time of 5.0 s. The dragster’s final speed is 130 m/s.Â Neglecting friction, what average power was needed to produce this final speed?
- A) 140 hp
- B) 750 hp
- C) 1100 hp
- D) 7 Ã 10
^{4}hp - E) 5 Ã 10
^{5}hp

Ans:Â CDifficulty:Â HardSectionDef:Â Additional Problems Reference:Â Ref 6-5 A 12.5-kg crate slides along a horizontal frictionless surface at a constant speed of 4.0 m/s.Â The crate then slides down a frictionless incline and across a second horizontal surface as shown in the figure.

- What is the kinetic energy of the crate as it slides on the upper surface?
- A) 30 J
- B) 80 J
- C) 100 J
- D) 200 J
- E) 490 J

Ans:Â CRefer To:Â Ref 6-5Difficulty:Â MediumSectionDef:Â Additional Problems

- While the crate slides along the upper surface, how much gravitational potential energy does it have compared to what it would have on the lower surface?
- A) 80 J
- B) 100 J
- C) 240 J
- D) 370 J
- E) 490 J

Ans:Â DRefer To:Â Ref 6-5Difficulty:Â MediumSectionDef:Â Additional Problems

- What is the speed of the crate when it arrives at the lower surface?
- A) 7 m/s
- B) 6 m/s
- C) 59 m/s
- D) 75 m/s
- E) 98 m/s

Ans:Â BRefer To:Â Ref 6-5Difficulty:Â MediumSectionDef:Â Additional Problems

- What is the kinetic energy of the crate as it slides on the lower surface?
- A) 290 J
- B) 320 J
- C) 370 J
- D) 470 J
- E) 570 J

Ans:Â DRefer To:Â Ref 6-5Difficulty:Â MediumSectionDef:Â Additional Problems

- What minimum coefficient of kinetic friction is required to bring the crate to a stop over a distance of 5.0 m along the lower surface?
- A) 30
- B) 32
- C) 60
- D) 66
- E) 76

Ans:Â ERefer To:Â Ref 6-5Difficulty:Â HardSectionDef:Â Additional Problems Reference:Â Ref 6-6 A rope exerts a force on a 20.0-kg crate.Â The crate starts from rest and accelerates upward at 5.00 m/s^{2} near the surface of the earth.

- What is the kinetic energy of the crate when it is 4.0 m above the floor?
- A) 400 J
- B) 250 J
- C) 116 J
- D) 704 J
- E) 1180 J

Ans:Â ARefer To:Â Ref 6-6Difficulty:Â HardSectionDef:Â Additional Problems

- How much work was done by the force in raising the crate 4.0 m above the floor?
- A) 399 J
- B) 250 J
- C) 116 J
- D) 704 J
- E) 1180 J

Ans:Â ERefer To:Â Ref 6-6Difficulty:Â MediumSectionDef:Â Additional Problems Reference:Â Ref 6-7 A 325-N force accelerates a 50.0-kg crate from rest along a horizontal frictionless surface for a distance of 20.0 m as shown in the figure.

- What is the final speed of the crate?
- A) 4 m/s
- B) 1 m/s
- C) 2 m/s
- D) 131 m/s
- E) 259 m/s

Ans:Â BRefer To:Â Ref 6-7Difficulty:Â HardSectionDef:Â Additional Problems

- How much work is done on the crate?
- A) 62 Ã 10
^{2}J - B) 70 Ã 10
^{2}J - C) 82 Ã 10
^{3}J - D) 50 Ã 10
^{3}J - E) 50 Ã 10
^{4}J

Ans:Â DRefer To:Â Ref 6-7Difficulty:Â MediumSectionDef:Â Additional Problems

- What coefficient of friction would be required to keep the crate moving at constant speed under the action of the 325-N force?
- A) 250
- B) 321
- C) 508
- D) 663
- E) 747

Ans:Â DDifficulty:Â HardSectionDef:Â Additional Problems Import Settings:Base Settings: Brownstone DefaultInformation Field: DifficultyInformation Field: SectionDefHighest Answer Letter: EMultiple Keywords in Same Paragraph: No Chapter: Chapter 7 Multiple Choice

- Which one of the following statements concerning momentum is true?
- A) Momentum is a force.
- B) Momentum is a scalar quantity.
- C) The SI unit of momentum is kg Ã m
^{2}/s. - D) The momentum of an object is always positive.
- E) Momentum and impulse are measured in the same units.

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 7-1

- A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements concerning the rock as it falls is true?Â Neglect the effects of air resistance.
- A) The rock will gain an equal amount of momentum during each second.
- B) The rock will gain an equal amount of kinetic energy during each second.
- C) The rock will gain an equal amount of speed for each meter through which it falls.
- D) The rock will gain an equal amount of momentum for each meter through which it falls.
- E) The amount of momentum the rock gains will be proportional to the amount of potential energy that it loses.

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 7-1

- A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which one of the following best describes why no injury occurs?
- A) The bag provides the necessary force to stop the person.
- B) The bag reduces the impulse to the person.
- C) The bag increases the amount of time the force acts on the person and reduces the change in momentum.
- D) The bag decreases the amount of time during which the momentum is changing and reduces the average force on the person.
- E) The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.

Ans:Â EDifficulty:Â HardSectionDef:Â Section 7-1

- Jennifer is walking at 1.22 m/s. If Jennifer weighs 552 N, what is the magnitude of her momentum?
- A) 0 kg Ã m/s
- B) 137 kg Ã m/s
- C) 6 kg Ã m/s
- D) 672 kg Ã m/s
- E) 951 kg Ã m/s

Ans:Â CDifficulty:Â EasySectionDef:Â Section 7-1

- A 1.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. What is the change in momentum of the ball?
- A) zero kg Ã m/s
- B) 12 kg Ã m/s, downward
- C) 12 kg Ã m/s, upward
- D) 24 kg Ã m/s, downward
- E) 24 kg Ã m/s, upward

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 7-1

- A projectile is launched with a momentum of 200 kg âĸ m/s and 1000 J of kinetic energy. What is the mass of the projectile?
- A) 5 kg
- B) 10 kg
- C) 20 kg
- D) 40 kg
- E) 50 kg

Ans:Â CDifficulty:Â HardSectionDef:Â Section 7-1

- A 0.2-kg steel ball is dropped straight down onto a hard, horizontal floor and bounces straight up. The ball’s speed just before
*and just after*impact with the floor is 10 m/s.Â Determine the magnitude of the impulse delivered to the floor by the steel ball. - A) zero N Ã s
- B) 2 N Ã s
- C) 4 N Ã s
- D) 20 N Ã s
- E) 200 N Ã s

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 7-1

- A machine gun fires 25-g bullets at the rate of 4 bullets per second. The bullets leave the gun at a speed of 1000 m/s.Â What is the average recoil force experienced by the machine gun?
- A) 10 N
- B) 20 N
- C) 100 N
- D) 200 N
- E) 1000 N

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 7-1

- A 0.065-kg tennis ball moving to the right with a speed of 15 m/s is struck by a tennis racket, causing it to move to the left with a speed of 15 m/s. If the ball remains in contact with the racquet for 0.020 s, what is the magnitude of the average force exerted on the ball?
- A) zero newtons
- B) 98 N
- C) 160 N
- D) 240 N
- E) 320 N

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 7-1

- A baseball of mass
*m*, initially at rest, is struck by a bat so that it acquires a speed*v*. If*t*represents the duration of the collision between the bat and the ball, which one of the following expressions determines the magnitude of the average force exerted on the ball? - A) (1/2)
*mv*^{2} - B)
*mv/t* - C) (1/2)
*mv*^{2}t - D)
*mt*^{2}/(2*v*) - E)
*mvt*

Ans:Â BDifficulty:Â EasySectionDef:Â Section 7-1

- An airplane is traveling at 225 m/s when it strikes a weather balloon (
*m*= 1.82 kg), which can be considered to be at rest relative to the ground below. After the collision, the balloon is caught on the fuselage and is traveling with the airplane.Â The collision takes place over a time interval ofÂ Â 4.44 Ã 10^{â3 }N.Â What is the average force that the balloon exerts on the airplane during the collision? - A) 415 N
- B) 78 Ã 10
^{4}N - C) 22 Ã 10
^{4}N - D) 61 Ã 10
^{5}N - E) 07 Ã 10
^{6}N

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 7-1

- While a car is stopped at a traffic light in a storm, raindrops strike the roof of the car. The area of the roof is 5.0 m
^{2}.Â Each raindrop has a mass of 3.7 Ã 10^{â4}kg and speed of 2.5 m/s before impact and is at rest after the impact.Â If, on average at a given time, 150 raindrops strike each square meter, what is the impulse of the rain striking the car? - A) 69 N Ã s
- B) 046 N Ã s
- C) 14 N Ã s
- D) 11 N Ã s
- E) 21 N Ã s

Ans:Â ADifficulty:Â HardSectionDef:Â Section 7-1

- A bat strikes a 0.050-kg baseball so that its velocity changes by +32 m/s in 0.080 s. With what average force was the ball struck?
- A) +20 N
- B) â20 N
- C) +200 N
- D) â200 N
- E) +10 N

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 7-1

- The head of a hammer (
*m*= 1.5 kg) moving at 4.5 m/s strikes a nail and bounces back with the same speed after an elastic collision lasting 0.075 s. What is the magnitude of the average force the hammer exerts on the nail? - A) 8 N
- B) 60 N
- C) 90 N
- D) 180 N
- E) 240 N

Ans:Â DDifficulty:Â HardSectionDef:Â Section 7-1

- A football player kicks a 0.41-kg football initially at rest; and the ball flies through the air. If the kicker’s foot was in contact with the ball for 0.051 s and the ball’s initial speed after the collision is 21 m/s, what was the magnitude of the average force on the football?
- A) 7 N
- B) 46 N
- C) 81 N
- D) 170 N
- E) 210 N

Ans:Â DDifficulty:Â HardSectionDef:Â Section 7-1 Reference:Â Ref 7-1 A 4.0-kg block slides along a frictionless surface with a constant speed of 5.0 m/s as shown.Â Two seconds *after* it begins sliding, a horizontal, time-dependent force is applied to the mass.Â The force is removed eight seconds later.Â The graph shows how the force on the block varies with time.

- What is the magnitude of the total impulse of the force acting on the block?
- A) 20 N Ã s
- B) 42 N Ã s
- C) 48 N Ã s
- D) 54 N Ã s
- E) 60 N Ã s

Ans:Â BRefer To:Â Ref 7-1Difficulty:Â MediumSectionDef:Â Section 7-1

- What, approximately, is the speed of the block at
*t*= 11 seconds? - A) 0 m/s
- B) 16 m/s
- C) 25 m/s
- D) 65 m/s
- E) 75 m/s

Ans:Â BRefer To:Â Ref 7-1Difficulty:Â HardSectionDef:Â Section 7-1

- In which one of the following situations is linear momentum
*not conserved*? - A) A bomb suspended by a string explodes into one hundred fragments.
- B) A bowling ball collides with a set of ten pins.
- C) A golf ball is struck by a club.
- D) An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction.
- E) A tree limb is struck by lightning and falls to the ground.

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 7-2

- A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force due to gravity is zero newtons.Â Which one of the following statements concerning this event is true?
- A) Kinetic energy is conserved in this process.
- B) All of the fragments must have equal kinetic energies.
- C) The sum of the kinetic energies of the fragments must be zero.
- D) The vector sum of the linear momenta of the fragments must be zero.
- E) The mass of any one fragment must be equal to the mass of any other fragment.

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 7-2

- An object of mass 3
*m*, initially at rest, explodes breaking into two fragments of mass*m*and 2*m,*respectively. Which one of the following statements concerning the fragments*after the explosion*is true? - A) They will fly off at right angles.
- B) They will fly off in the same direction.
- C) The smaller fragment will have twice the speed of the larger fragment.
- D) The larger fragment will have twice the speed of the smaller fragment.
- E) The smaller fragment will have four times the speed of the larger fragment.

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 7-2

- A 100-kg cannon at rest contains a 10-kg cannon ball. When fired, the cannon ball leaves the cannon with a speed of 90 m/s.Â What is the recoil speed of the cannon?
- A) 5 m/s
- B) 9 m/s
- C) 45 m/s
- D) 90 m/s
- E) zero m/s

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 7-2

- A 50-kg toboggan is coasting on level snow. As it passes beneath a bridge, a 20-kg parcel is dropped straight down and lands in the toboggan.Â If KE
_{1}is the original kinetic energy of the toboggan and KE_{2}is the kinetic energy after the parcel has been added, what is the ratio KE_{2}/KE_{1}. - A) 4
- B) 6
- C) 7
- D) 8
- E) 1

Ans:Â CDifficulty:Â HardSectionDef:Â Section 7-2

- A sled of mass
*m*is coasting on the icy surface of a frozen river. While it is passing under a bridge, a package of equal mass*m*Â is dropped straight down and lands on the sled (without causing any damage).Â The sled plus the added load then continue along the original line of motion.Â How does the kinetic energy of the (sled + load) compare with the original kinetic energy of the sled? - A) It is 1/4 the original kinetic energy of the sled.
- B) It is 1/2 the original kinetic energy of the sled.
- C) It is 3/4 the original kinetic energy of the sled.
- D) It is the same as the original kinetic energy of the sled.
- E) It is twice the original kinetic energy of the sled.

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 7-2

- A bullet of mass
*m*is fired at speed*v*into a wooden block of mass_{0}*M*. The bullet instantaneously comes to rest in the block.Â The block with the embedded bullet slides along a horizontal surface with a coefficient of kinetic friction m.

Which one of the following expressions determines how far the block slides before it comes to rest (the magnitude of displacement **s** in the figure)?

- A)
- B)
- C)
- D)
- E)

Ans:Â CDifficulty:Â HardSectionDef:Â Section 7-2

- While in Earth’s orbit, an 80-kg astronaut carrying a 20-kg tool kit is initially drifting toward a stationary (relative to her) space shuttle at a speed of 2 m/s. If she throws the tool kit toward the shuttle with a speed of 6 m/s as seen from the shuttle, her final speed is
- A) 1 m/s toward the shuttle.
- B) 1 m/s away from the shuttle.
- C) 2 m/s toward the shuttle.
- D) 4 m/s toward the shuttle.
- E) 6 m/s away from the shuttle.

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 7-2

- While on an interplanetary mission, a 58.5-kg astronaut is floating toward the front of her ship at 0.15 m/s, relative to the ship. She wishes to stop moving, relative to the ship.Â She decides to throw away the 2.50-kg book she’s carrying.Â What should the approximate speed and direction of the book be to achieve her goal?
- A) 15 m/s, toward the front of the ship
- B) 5 m/s, toward the back of the ship
- C) 7 m/s, toward the front of the ship
- D) 30 m/s, toward the back of the ship
- E) 5 m/s, toward the front of the ship

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 7-2

- Complete the following statement: Different types of collisions between interacting bodies are
*categorized*on the basis of - A) kinetic energy conservation.
- B) mechanical energy conservation.
- C) linear momentum conservation.
- D) the magnitude of the forces involved.
- E) the temporal duration of the collision.

Ans:Â ADifficulty:Â EasySectionDef:Â Section 7-3 and 7-4

- Complete the following statement: A collision is
*elastic*if - A) the final velocities are zero.
- B) the objects stick together.
- C) the final kinetic energy is zero.
- D) the final momentum is zero.
- E) the total kinetic energy is conserved.

Ans:Â EDifficulty:Â EasySectionDef:Â Section 7-3 and 7-4

- Which one of the following is characteristic of an
*inelastic collision*? - A) Total mass is not conserved.
- B) Total energy is not conserved.
- C) Linear momentum is not conserved.
- D) Kinetic energy is not conserved.
- E) The change in momentum is less than the total impulse.

Ans:Â DDifficulty:Â EasySectionDef:Â Section 7-3 and 7-4

- Two objects of equal mass traveling toward each other with equal speeds undergo a head on collision. Which one of the following statements concerning their velocities
*after the collision*is*necessarily*true? - A) They will exchange velocities.
- B) Their velocities will be reduced.
- C) Their velocities will be unchanged.
- D) Their velocities will be zero.
- E) Their velocities may be zero.

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- Complete the following statement: Momentum will be conserved in a two-body collision
*only if* - A) both bodies come to rest.
- B) the collision is perfectly elastic.
- C) the kinetic energy of the system is conserved.
- D) the net external force acting on the two-body system is zero.
- E) the internal forces of the two body system cancel in action-reaction pairs.

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- Two objects of equal mass collide on a horizontal frictionless surface. Before the collision, object
**A**is at rest while object**B**has a constant velocity of 12 m/s.Â After the collision, the two objects are stuck together.Â What is the speed of the composite body (**A**+**B**) after the collision? - A) 0 m/s
- B) 0 m/s
- C) 12 m/s
- D) 24 m/s
- E) 36 m/s

Ans:Â BDifficulty:Â EasySectionDef:Â Section 7-3 and 7-4

- A 2-kg stone falls 100 meters near the surface of the earth. It strikes the ground without any rebound thereby making a completely inelastic collision with the earth.Â Approximately how much kinetic energy is transferred to the earth in this process?
- A) zero joules
- B) 200 J
- C) 2000 J
- D) 10 000 J
- E) 20 000 J

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A tennis ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. Which statement is true concerning this situation?
- A) The momentum of the ball and the momentum of the earth both change.
- B) Neither the momentum of the ball nor the momentum of the earth changes.
- C) The momentum of the ball is changed; and the momentum of the earth is not changed.
- D) The momentum of the ball is unchanged; and the momentum of the earth is changed.
- E) Both the momentum and the kinetic energy of the ball change because of the collision.

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A 3.0-kg cart moving to the right with a speed of 1.0 m/s has a head-on collision with a 5.0-kg cart that is initially moving to the left with a speed of 2.0 m/s. After the collision, the 3.0-kg cart is moving to the left with a speed of 1.0 m/s.Â What is the final velocity of the 5.0-kg cart?
- A) zero m/s
- B) 80 m/s to the right
- C) 80 m/s to the left
- D) 0 m/s to the right
- E) 0 m/s to the left

Ans:Â CDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A 1000-kg car traveling east at 20 m/s collides with a 1500-kg car traveling west at 10 m/s. The cars stick together after the collision.Â What is the common velocity of the cars after the collision?
- A) 16 m/s, east
- B) 6 m/s, west
- C) 4 m/s, east
- D) 2 m/s, east
- E) 1 m/s, west

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A 0.050-kg lump of clay moving horizontally at 12 m/s strikes
*and sticks to*a stationary 0.15-kg cart that can move on a frictionless air track. Determine the speed of the cart and clay after the collision. - A) zero m/s
- B) 3 m/s
- C) 6 m/s
- D) 9 m/s
- E) 12 m/s

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A 0.10-kg cart traveling in the positive
*x*direction at 10.0 m/s collides with a 0.30-kg cart at rest. The collision is elastic.Â What is the velocity of the 0.10-kg cart after the collision? - A) +2.5 m/s
- B) â2.5 m/s
- C) +5 m/s
- D) â5 m/s
- E) +3.3 m/s

Ans:Â DDifficulty:Â HardSectionDef:Â Section 7-3 and 7-4

- A 50.0-kg boy runs at a speed of 10.0 m/s and jumps onto a cart as shown in the figure. The cart is initially at rest.Â If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart?
- A) 150 kg
- B) 175 kg
- C) 210 kg
- D) 260 kg
- E) 300 kg

Ans:Â ADifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A 0.015-kg marble moving to the right at 0.40 m/s has a head-on, elastic collision with a 0.045-kg marble sitting at rest on a smooth, level surface. Which of the following are the correct magnitudes and directions of the velocities of the two marbles after the collision?

__0.015 kg marble__*Â Â Â Â Â Â Â Â Â 0.045 kg marble*

- A) 15 m/s, leftÂ Â Â Â Â Â 0.25 m/s, right
- B) 10 m/s, rightÂ Â Â Â 0.30 m/s, right
- C) zero m/sÂ Â Â Â Â Â Â Â Â Â Â Â Â Â 25 m/s, right
- D) 20 m/s, leftÂ Â Â Â Â Â 0.20 m/s, right
- E) 40 m/s, leftÂ Â Â Â Â Â zero m/s

Ans:Â DDifficulty:Â HardSectionDef:Â Section 7-3 and 7-4

- A 7.30-kg bowling ball strikes a 1.60-kg pin at rest head-on. Before the collision, the velocity of the ball is +6.00 m/s.Â After the collision, the velocity of the ball is +5.40 m/s.Â What is the velocity of the pin after the collision?
- A) +0.6 m/s
- B) +5.4 m/s
- C) +1.2 m/s
- D) +2.7 m/s
- E) +3.2 m/s

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- A 2.5-kg ball and a 5.0-kg ball have an elastic collision. Before the collision, the 2.5-kg ball was at rest and the other ball had a speed of 3.5 m/s.Â What is the kinetic energy of the 2.5-kg ball after the collision?
- A) 7 J
- B) 4 J
- C) 1 J
- D) 14 J
- E) 27 J

Ans:Â EDifficulty:Â HardSectionDef:Â Section 7-3 and 7-4

- Two objects constitute an isolated system. In an elastic collision between the two objects, which one of the following statements is a false statement?
- A) The total kinetic energy is conserved.
- B) The kinetic energy of each object is the same before and after the collision.
- C) The total momentum is conserved.
- D) The magnitude of the force exerted by each object on the other object is equal.
- E) The total kinetic energy before the collision is equal to the total kinetic energy after the collision.

Ans:Â BDifficulty:Â EasySectionDef:Â Section 7-3 and 7-4

- A 35-kg girl is standing near and to the left of a 43-kg boy on the frictionless surface of a frozen pond. The boy throws a 0.75-kg ice ball to the girl with a horizontal speed of 6.2 m/s.Â What are the velocities of the boy and the girl immediately after the girl catches the ice ball?

girlÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â boy

- A) 81 m/s, left 0.67 m/s, right
- B) 17 m/s, left 0.14 m/s, left
- C) 18 m/s, right 0.13 m/s, left
- D) 42 m/s, left 0.49 m/s, right
- E) 13 m/s, left 0.11 m/s, right

Ans:Â EDifficulty:Â HardSectionDef:Â Section 7-3 and 7-4 Reference:Â Ref 7-2 A comet fragment of mass 1.96 Ã 10^{13} kg is moving at 6.50 Ã 10^{4} m/s when it crashes into Callisto, a moon of Jupiter.Â The mass of Callisto is 1.08 Ã 10^{23} kg.Â The collision is completely inelastic.

- Assuming for this calculation that Callisto’s initial momentum is zero kg Ã m/s, what is the recoil speed of Callisto immediately after the collision?
- A) 34 Ã 10
^{â18}m/s - B) 27 Ã 10
^{â14}m/s - C) 58 Ã 10
^{â12}m/s - D) 13 Ã 10
^{â7}m/s - E) 18 Ã 10
^{â5}m/s

Ans:Â ERefer To:Â Ref 7-2Difficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- How much kinetic energy was released in the collision?
- A) 28 Ã 10
^{22}J - B) 51 Ã 10
^{27}J - C) 02 Ã 10
^{27}J - D) 14 Ã 10
^{22}J - E) 50 Ã 10
^{13}J

Ans:Â DRefer To:Â Ref 7-2Difficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- Car One is traveling due north and Car Two is traveling due east. After the collision shown, Car One rebounds in the due south direction.Â Which of the numbered arrows is the only one that can represent the final direction of Car Two?
- A) 1
- B) 2
- C) 3
- D) 4
- E) 5

Ans:Â DDifficulty:Â EasySectionDef:Â Section 7-3 and 7-4

- A 0.50-kg bomb is sliding along an icy pond (frictionless surface) with a velocity of 2.0 m/s to the west. The bomb explodes into two pieces.Â After the explosion, a 0.20-kg piece moves south at 4.0 m/s.Â What are the components of the velocity of the 0.30-kg piece?
- A) 0 m/s north, 0 m/s
- B) 7 m/s north, 3.3 m/s west
- C) 0 m/s north, 2.7 m/s west
- D) 0 m/s, 2.0 m/s east
- E) 0 m/s north, 2.0 m/s east

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 7-3 and 7-4

- Two asteroids are drifting in space with trajectories shown. Assuming the collision at point
*O*between them is completely inelastic, at what angle from its original direction is the larger asteroid deflected? - A) 80Â° above the +
*x*axis - B) 69Â° above the +
*x*axis - C) 42Â° above the +
*x*axis - D) 47Â° above the +
*x*axis - E) 90Â° above the +
*x*axis

Ans:Â ADifficulty:Â HardSectionDef:Â Section 7-3 and 7-4

- In the game of billiards, all the balls have approximately the same mass, about 0.17 kg. In the figure, the cue ball strikes another ball such that it follows the path shown.Â The other ball has a speed of 1.5 m/s immediately after the collision.Â What is the speed of the cue ball after the collision?
- A) 5 m/s
- B) 8 m/s
- C) 6 m/s
- D) 3 m/s
- E) 2 m/s

Ans:Â CDifficulty:Â HardSectionDef:Â Section 7-3 and 7-4

- Which one of the following statements concerning center of mass is true?
- A) All of an object’s mass is located at its center of mass.
- B) The center of mass of an object must be located within the object.
- C) The center of mass of a system of objects cannot change even if there are forces acting on the objects.
- D) The velocity of the center of mass of a system of objects is greatly affected by a collision of objects within the system.
- E) The velocity of the center of mass of a system of objects is constant when the sum of the external forces acting on the system is zero.

Ans:Â EDifficulty:Â MediumSectionDef:Â Section 7-5

- The drawing shows two 4.5-kg balls located on the
*y*axis at 1.0 and 9.0 m, respectively, and a third ball with a mass 2.3 kg which is located at 6.0 m. What is the location of the center of mass of this system? - A) 8 m
- B) 2 m
- C) 6 m
- D) 0 m
- E) 4 m

Ans:Â BDifficulty:Â MediumSectionDef:Â Section 7-5

- During hockey practice, two pucks are sliding across the ice in the same direction. At one instant, a 0.18-kg puck is moving at 16 m/s while the other puck has a mass of 0.14 kg and a speed of 3.8 m/s.Â What is the velocity of the center of mass of the two pucks?
- A) 0 m/s
- B) 0 m/s
- C) 0 m/s
- D) 11 m/s
- E) 13 m/s

Ans:Â DDifficulty:Â MediumSectionDef:Â Section 7-5

- A juggler demonstrates his abilities by keeping a 2.3-kg pipe wrench, a 1.5-kg hatchet, and a 1.0-kg hammer flying through the air above his head. The white circles on the graph represent the positions of the center of mass of each of the flying objects at one instant.Â What are the
*x*and*y*coordinates of the center of mass forÂ the system of these three objects?

*xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â y*

- A) 46 m 0.47 m
- B) 30 m 0.54 m
- C) 42 m 0.60 m
- D) 47 m 0.26 m
- E) 60 m 0.42 m

Ans:Â ADifficulty:Â HardSectionDef:Â Section 7-5 Reference:Â Ref 7-3 A space vehicle of mass *m* has a speed *v*.Â At some instant, it separates into two pieces, each of mass 0.5*m*.Â One of the pieces is at rest just after the separation.

- Which one of the following statements concerning this situation is true?
- A) The moving piece has speed 2
*v*. - B) This process conserves kinetic energy.
- C) The piece at rest possesses kinetic energy.
- D) The process does not conserve total energy.
- E) This process does not conserve momentum.

Ans:Â ARefer To:Â Ref 7-3Difficulty:Â EasySectionDef:Â Additional Problems

- What is the kinetic energy of the moving piece just after the separation?
- A) zero joules
- B)
- C)
- D)
*mv*^{2} - E) 2
*mv*^{2}

Ans:Â DRefer To:Â Ref 7-3Difficulty:Â EasySectionDef:Â Additional Problems

- How much work was done by the internal forces that caused the separation?
- A) zero joules
- B)
- C)
- D)
*mv*^{2} - E) 2
*mv*^{2}

Ans:Â CRefer To:Â Ref 7-3Difficulty:Â MediumSectionDef:Â Additional Problems

- A mother is holding her 4.5-kg baby in her arms while riding in a car moving at 22 m/s. The car is involved in a head-on collision and stops within 1.5 seconds.Â What is the magnitude of the force exerted by the baby on his mother’s arms?
- A) 45 N
- B) 66 N
- C) 90 N
- D) 99 N
- E) 150 N

Ans:Â BDifficulty:Â MediumSectionDef:Â Additional Problems

- A rocket is launched vertically from rest; and it burns fuel at a constant rate of 136 kg/s. Exhaust gases are expelled with a speed of 5.25 Ã 10
^{3 }m/s relative to the rocket.Â What is the magnitude of the thrust? - A) 14 Ã 10
^{5}N - B) 64 Ã 10
^{6}N - C) 59 Ã 10
^{â2}N - D) 808 N
- E) 6 N

Ans:Â ADifficulty:Â MediumSectionDef:Â Additional Problems

- A 100-kg fisherman and a 500-kg supply crate are on a frozen pond that is essentially frictionless. The man and the crate are initially separated by a distance of 600 meters.Â The fisherman uses a very light rope to pull the crate closer to him.Â How far has the man moved when the crate reaches the fisherman?
- A) zero meters
- B) 10 m
- C) 50 m
- D) 100 m
- E) 500 m

Ans:Â EDifficulty:Â MediumSectionDef:Â Additional Problems

- A 160-kg space probe is moving in the positive
*x*direction at 18 km/s when it encounters a time-dependent force directed in the negative*x*direction. The force is as follows:

Determine the final speed of the space probe.

- A) 6 km/s
- B) 3 km/s
- C) 11 km/s
- D) 16 km/s
- E) 23 km/s

Ans:Â ADifficulty:Â MediumSectionDef:Â Additional Problems Reference:Â Ref 7-4 A 2.0-kg pistol fires a 1.0-g bullet with a muzzle speed of 1000 m/s.Â The bullet then strikes a 10-kg wooden block resting on a horizontal frictionless surface.Â The block and the embedded bullet then slide across the surface.

- What is the kinetic energy of the bullet as it travels toward the block?
- A) 100 J
- B) 500 J
- C) 1000 J
- D) 5000 J
- E) 10 000 J

Ans:Â BRefer To:Â Ref 7-4Difficulty:Â EasySectionDef:Â Additional Problems

- The explosive charge in the pistol acts for 0.001 s. What is the average force exerted on the bullet while it is being fired?
- A) 001 N
- B) 0 N
- C) 100 N
- D) 500 N
- E) 1000 N

Ans:Â ERefer To:Â Ref 7-4Difficulty:Â MediumSectionDef:Â Additional Problems

- What is the speed of the “bullet + block” system immediately after the bullet is embedded in the block?
- A) 1 m/s
- B) 10 m/s
- C) 1000 m/s
- D) 10 000 m/s
- E) zero m/s

Ans:Â ARefer To:Â Ref 7-4Difficulty:Â MediumSectionDef:Â Additional Problems Reference:Â Ref 7-5 A stationary 4-kg shell explodes into three pieces.Â Two of the fragments have a mass of 1 kg each and move along the paths shown with a speed of 10 m/s.Â The third fragment moves upward as shown.

- What is the speed of the third fragment?
- A) zero m/s
- B) 1 m/s
- C) 5 m/s
- D) 10 m/s
- E) 20 m/s

Ans:Â CRefer To:Â Ref 7-5Difficulty:Â MediumSectionDef:Â Additional Problems

- What is the speed of the center of mass of this system after the explosion?
- A) zero m/s
- B) 1 m/s
- C) 3 m/s
- D) 5 m/s
- E) 7 m/s

Ans:Â ARefer To:Â Ref 7-5Difficulty:Â MediumSectionDef:Â Additional Problems