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Chapter 3 Momentum and Energy

3.1 Momentum and Impulse

1) Which of the following has the largest momentum relative to Earth?

A) a tightrope walker crossing Niagara Falls

B) a pickup truck speeding along a highway

C) a Mack truck parked in a lot

D) a dog running down the street

Answer: B

2) A freight train rolls along a track with considerable momentum. If it rolls at the same speed

but has twice as much mass, its momentum is

A) zero.

B) doubled.

C) quadrupled.

D) unchanged.

Answer: B

3) An object in motion will continue in motion with

A) acceleration.

B) impulse.

C) momentum.

D) all of the above

E) none of the above

Answer: C

4) From the same height you simultaneously drop a lightweight tennis ball and a heavyweight

bowling ball. When they hit the floor they have the same

A) speed.

B) force.

C) momentum.

D) all of the above

E) none of the above

Answer: A

5) A heavy truck and a small truck roll down a hill. Neglecting friction, at the bottom of the hill

the heavy truck has greater

A) speed.

B) acceleration.

C) momentum.

D) all of the above

E) none of the above

Answer: C

6) A 4-kg ball has a momentum of 12 kg∙m/s. What is the ball's speed?

A) 3 m/s

B) 4 m/s

C) 12 m/s

D) 48 m/s

E) none of the above

Answer: A

7) A ball is moving at 4 m/s and has a momentum of 48 kg∙m/s. What is the ball's mass?

A) 4 kg

B) 12 kg

C) 48 kg

D) 192 kg

E) none of the above

Answer: B

8) In terms of momentum, why is a drinking glass less likely to break if it falls on a carpet floor

than falling on a hard concrete floor?

Answer: The carpet floor has more "give," which means it takes more time for the momentum of

the falling glass to reduce to zero as it hits the surface. More time means less force, which means

less chance of breaking upon contact.

9) An unfortunate bug splatters on the windshield of a moving car. Describe the forces, impulses,

momentum changes, and accelerations of both the bug and the car.

Answer: According to Newton's third law, the force of collision will be the same on both the bug

and the car, but will act in opposite directions. The time during which the force acts is the same

on both, so the impulses on the bug and the car will be equal in magnitude but opposite in

direction. This means that each will undergo equal and opposite changes in momentum. (It is

important to stress that the momentum and the bug are not the same, but they change by the same

amount! The car loses as much momentum as the bug gains in the collision.) Because of the

small mass of the bug, its acceleration will be very large. Because of the large mass of the car, its

acceleration (deceleration) will be unnoticeable.

10) A boy fires a spring-loaded Ping-Pong ball gun. Briefly compare the forces and impulses on

the gun and the ball. Which has more momentum? Which moves faster?

Answer: Both force and impulse on both the ball and gun are equal and opposite. So they both

undergo equal and opposite changes in momentum. Since they begin with no momentum, they

have equal and opposite momentum as the ball fires and the gun recoils. Since the ball is less

massive, it has the greater acceleration for the same force, and therefore moves faster.

11) A diesel locomotive coasting at 10 km/h runs into a stationary flatcar. The locomotive

weighs four times as much as the flatcar. How fast do the locomotive and flatcar move when

they stick together upon collision?

Answer: Momentum before collision = momentum after collision.

masslocomotive × 10 km/h. = (masslocomotive + massflatcar) × v.

So v = masslocomotive / (masslocomotive + massflatcar) × 10 km/h. Or,

v = 4 massflatcar/5 massflatcar × 10 km/h = 8 km/h.

3.2 Impulse Changes Momentum

1) The distinction between impulse and force involves the

A) distance the force acts.

B) time the force acts.

C) difference between acceleration and velocity.

D) mass and its effect on resisting a change in momentum.

Answer: B

2) It is correct to say that impulse is equal to

A) momentum.

B) the change in momentum.

C) the force multiplied by the distance the force acts.

D) all of the above

E) none of the above

Answer: B

3) The impulse-momentum relationship is a direct result of

A) Newton's first law.

B) Newton's second law.

C) Newton's third law.

Answer: B

4) In order to catch a fast-moving softball with your bare hand, you extend your hand forward

just before the catch and then let the ball ride backward with your hand. Doing this reduces the

catching force because the

A) relative velocity is less.

B) relative velocity is more.

C) time of catch is increased.

D) time of the catch is decreased.

E) none of the above

Answer: C

5) When you jump from an elevated position you usually bend your knees upon reaching the

ground. By doing this, the contact time is about 10 times more than for a stiff-legged landing and

the average force your body experiences is reduced by

A) less than 10 times.

B) more than 10 times.

C) about 10 times.

Answer: C

6) When you are in the way of a fast-moving object and can't get escape, you will suffer a

smaller force if the collision time is

A) long.

B) short.

C) the same way either way.

Answer: A

7) A car traveling along the highway needs a certain amount of braking force to stop. More

braking force is required when the car has

A) more mass.

B) more momentum.

C) less stopping distance.

D) all of the above

E) none of the above

Answer: D

8) Padded dashboards in cars are safer in an accident than non-padded ones because an occupant

hitting the dash has

A) increased time of contact.

B) decreased contact force.

C) both

D) neither of these

Answer: C

9) The force of a falling apple hitting the ground depends upon

A) the speed of the apple just before it hits.

B) the time of contact with the ground.

C) whether or not the apple bounces.

D) all of the above

Answer: D

10) Compared with falling on a wooden floor, a wine glass may not break when it falls on a

carpeted floor because of

A) lesser impulse in stopping.

B) longer time to stop.

C) both

D) neither

Answer: B

11) According to the impulse—momentum equation Ft = change in mv, a bungee jumper in fall

has momentum which is reduced by the force F exerted by the bungee cord. If m is the mass of

the jumper, then v in the equation is the speed of the

A) jumper.

B) cord.

C) both

D) none of the above

Answer: A

12) A 1000-kg car moving at 10 m/s that brakes to a stop in 5 s has an average braking force of

A) 1000 N.

B) 2000 N.

C) 3000 N.

D) 4000 N.

E) 5000 N.

Answer: B

13) A boxer punches a sheet of paper in midair from rest to a speed of 40 m/s in 0.05 s. If the

mass of the paper is 0.01 kg, the force of the punch on the paper is

A) 0.08 N.

B) 0.8 N.

C) 8.0 N.

D) 80 N.

Answer: C

14) Consider driving into a massive concrete wall with no "give," versus having a head-on

collision at the same speed with an identical car moving toward you at the same speed. It would

be more damaging to hit the

A) car.

B) wall.

C) the same

Answer: C

3.3 Conservation of Momentum

1) The conservation of momentum is closely related to

A) Newton's first law.

B) Newton's second law.

C) Newton's third law.

Answer: C

2) A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the

same amount of time. Compared with the force to stop the car, the force needed to stop the truck

is

A) greater.

B) smaller.

C) the same.

Answer: A

3) The force that accelerates a rocket in outer space is exerted on the rocket by the

A) rocket's engine.

B) rocket's wings.

C) atmospheric pressure.

D) exhaust gases.

E) none of the above

Answer: D

4) When a cannon fires a cannonball at a given speed, the smaller recoil speed of the cannon is

due to different

A) forces.

B) times.

C) masses.

D) momenta.

Answer: C

5) Suppose a gun were made of strong lightweight material with a pellet that is more massive

than the gun. Then firing speed is greater for the

A) pellet.

B) recoiling gun.

C) both are the same

D) none of the above

Answer: B

6) The speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun

A) when momentum is conserved.

B) because velocity is conserved.

C) when both velocity and momentum are conserved.

D) if the masses of the bullet and gun are equal.

E) none of the above

Answer: D

7) Recoil is noticeable if we throw a heavy ball while standing on a skateboard. If instead we go

through the throwing motion but hold onto the ball, without friction effects our net recoil will be

A) zero.

B) the same as before.

C) small, but noticeable.

Answer: A

8) When bullets are fired from an airplane in the forward direction of motion, the momentum of

the airplane

A) decreases.

B) is unchanged.

C) increases.

Answer: A

9) A karate expert executes a swift blow and severs a brick with her bare hand. Equal magnitudes

occur for the

A) impulse on both the brick and the expert's hand.

B) force on both the brick and the expert's hand.

C) time of contact on both the block and the expert's hand.

D) all of the above

E) none of the above

Answer: D

10) A 5000-kg freight car crashes into a 10,000-kg freight car at rest. They couple upon collision

and move with a speed of 2 m/s. What was the initial speed of the 5000-kg freight car?

A) 4 m/s

B) 5 m/s

C) 6 m/s

D) 8 m/s

E) none of the above

Answer: C

11) Two identical freight cars roll without friction towards each other on a level track. One car

rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide, they couple and roll together

with a speed of

A) 0.5 m/s.

B) 0.33 m/s.

C) 0.67 m/s.

D) 1.0 m/s.

E) none of the above

Answer: A

12) A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at

12 m/s collides with it and they both stick together and move at a speed of

A) 3 m/s.

B) 4 m/s.

C) 6 m/s.

D) 8 m/s.

E) none of the above

Answer: E

13) You're driving down the highway and a lovebug spatters onto your windshield. Which

undergoes the greater impulse?

A) the lovebug

B) your car

C) both the same

Answer: C

14) You're driving down the highway and a lovebug spatters onto your windshield. Which

undergoes the greater change in momentum?

A) the lovebug

B) your car

C) both the same

Answer: C

15) You're driving down the highway and a lovebug spatters onto your windshield. Which

undergoes the greater force of impact?

A) the lovebug

B) your car

C) both the same

Answer: C

16) Two billiard balls having the same mass roll toward each other at the same speed. What is

the net momentum of the two-ball system?

A) 0 kg∙m/s

B) 10 kg∙m/s

C) not enough information

Answer: A

17) You use a straw for a pea shooter. The speed of the pea emerging from the straw when you

blow through it will be greater if the straw is

A) cut in half.

B) full length.

C) either cut in half or full length.

Answer: B

18) A cannonball fired from a long-barrel cannon will have a greater muzzle velocity because the

cannonball receives a greater

A) force.

B) impulse.

C) both

D) neither

Answer: B

19) A rifle of mass 2 kg is horizontally suspended by a pair of strings so that recoil can be

measured. The rifle fires a bullet of mass 1/100 kg at a speed of 200 m/s. The recoil velocity of

the rifle is about

A) 0.001 m/s.

B) 0.01 m/s.

C) 0.1 m/s.

D) 1 m/s.

E) none of the above

Answer: D

20) A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The

speed of the larger fish after lunch is

A) 1/2 m/s.

B) 2/5 m/s.

C) 5/6 m/s.

D) 6/5 m/s.

E) 1 m/s.

Answer: C

21) A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish swimming

toward it at 4 m/s. The speed of the larger fish after lunch is

A) 1/2 m/s.

B) 1/5 m/s.

C) 1/6 m/s.

D) 2/3 m/s.

E) 3/2 m/s.

Answer: C

22) A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is

initially at rest in space. The bowling ball and putty are then set in motion with a speed of

A) 1/4 m/s.

B) 1/5 m/s.

C) 1/6 m/s.

D) none of the above

E) not enough information

Answer: C

23) A 0.5-kg blob of clay moving at 2.0 m/s slams into a 4.0-kg blob of clay at rest. The speed of

the two blobs stuck together after colliding is about

A) 1.1 m/s.

B) 1.5 m/s.

C) 2.5 m/s.

D) none of the above

Answer: D

24) A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball

that is initially at rest. After the putty sticks to the ball, both move with a combined momentum

of

A) less than 1 unit.

B) more than 1 unit.

C) 1 unit.

D) not enough information

Answer: C

25) A 1-kg chunk of putty moving at 1 m/s collides and sticks to a 5-kg bowling ball initially at

rest. The bowling ball and putty move with a momentum of

A) 0 kg∙m/s.

B) 1 kg∙m/s.

C) 2 kg∙m/s.

D) 5 kg∙m/s.

E) more than 5 kg∙m/s.

Answer: B

26) A 30-kg girl and a 25-kg boy face each other on friction-free roller blades. The girl pushes

the boy, who moves away at a speed of 1.0 m/s. The girl's speed is

A) 0.45 m/s.

B) 0.55 m/s.

C) 0.83 m/s.

D) 1.2 m/s.

Answer: C

27) When a 100-kg astronaut ejects 0.1 kg of gas at a speed of 50 m/s from her propulsion pistol,

her recoil speed is

A) 50 m/s.

B) 5.0 m/s.

C) 0.5 m/s.

D) 0.05 m/s.

Answer: D

28) When an apple falls to the ground, momentum is transferred to the ground. The momentum

absorbed by the ground is

A) negligible compared to the momentum of the apple.

B) greater than that of the apple if the apple bounces.

C) greater than that of the apple in all cases.

D) none of the above

Answer: B

29) Suppose an astronaut in outer space plays a solitary game of "throw, bounce, and catch" by

tossing a ball against a very massive and perfectly elastic concrete wall.

A) The astronaut will catch the ball on one bounce only.

B) The astronaut will never catch the first bounce.

C) The astronaut's time between catches will decrease as the game progresses.

D) none of the above

Answer: B

30) Consider gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1

kg, a speed of 1 m/s, and collides with glider B, which has a mass of 5 kg and is at rest. If they

stick upon collision the speed the combined gliders will be

A) 1/4 m/s.

B) 1/5 m/s.

C) 1/6 m/s.

D) 1 m/s.

E) none of the above

Answer: C

31) A 1-kg glider and a 2-kg glider both slide toward each other at 1 m/s on an air track. They

collide and stick. The combined gliders move at

A) 0 m/s.

B) 1/2 m/s.

C) 1/3 m/s.

D) 1/6 m/s.

E) 1.5 m/s.

Answer: C

32) Two identical gliders slide toward each other on an air track. One glider moves at 1 m/s and

the other glider moves at 2 m/s. They collide and stick. The combined gliders move at

A) 1/2 m/s.

B) 1/3 m/s.

C) 1/6 m/s.

D) 3/4 m/s.

E) 1.5 m/s.

Answer: A

33) A 1-N apple falls to the ground. The apple hits the ground with a force of

A) 1 N.

B) 2 N.

C) 4 N.

D) 10 N.

E) not enough information

Answer: E

34) An open freight car rolls friction-free along a horizontal track in vertically pouring rain. As

water accumulates in the car, its speed

A) increases.

B) decreases.

C) doesn't change.

Answer: B

35) Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard.

Immediately after landing on the skateboard, Freddy's speed

A) increases.

B) decreases.

C) doesn't change.

Answer: B

3.4 Energy and Work

1) Whereas impulse involves the time that a force acts, work involves the

A) distance that a force acts.

B) time and distance that a force acts.

C) acceleration that a force produces.

Answer: A

2) If you push for an hour against a stationary wall, you do no work

A) on the wall.

B) at all.

C) both

D) none of the above

Answer: A

3) If you push an object twice as far while applying the same force, you do

A) twice as much work.

B) four times as much work.

C) the same amount of work.

Answer: A

4) When you push an object a certain distance while applying twice the force, you do

A) twice as much work.

B) four times as much work.

C) the same amount of work.

Answer: A

5) An object lifted 10 m gains a certain amount of potential energy. If it is lifted 20 m, its gain in

potential energy is

A) less.

B) the same.

C) twice as much.

D) four times as much.

E) more than four times as much.

Answer: C

6) A 1000-kg car and a 2000-kg car are hoisted the same distance in a service station. Raising the

more massive car requires

A) less work.

B) as much work.

C) twice as much work.

D) four times as much work.

E) more than four times as much work.

Answer: C

7) A moving object has

A) speed.

B) velocity.

C) momentum.

D) energy.

E) all of the above

Answer: E

8) If a charging rhinoceros has momentum, it must also have

A) potential energy.

B) kinetic energy.

C) work.

D) all of the above

Answer: B

9) An object that has kinetic energy must be

A) moving.

B) falling.

C) at an elevated position.

D) at rest.

E) none of the above

Answer: A

10) An object may have potential energy because of its

A) speed.

B) acceleration.

C) momentum.

D) location.

E) none of the above

Answer: D

11) A clerk can lift containers a vertical distance of 1 m, or roll them up a 2-m-long ramp to the

same elevation. With the ramp, the applied force needed is

A) half as much.

B) twice as much.

C) the same.

Answer: A

12) A bow is drawn so that it has 40 J of potential energy. When the arrow is fired its kinetic

energy is ideally

A) less than 40 J.

B) more than 40 J.

C) 40 J.

Answer: C

13) A music console is pushed a distance of 2 m with a force of 20 N. The work done on the

console is

A) 2 J.

B) 10 J.

C) 20 J.

D) 40 J.

E) 80 J.

Answer: D

14) It takes 40 J to push a large crate 4 m across a floor. The force exerted on the crate is

A) 4 N.

B) 10 N.

C) 40 N.

D) 160 N.

E) 1600 N.

Answer: B

15) A 2-kg mass weighs 20 N and is held 4 m above the ground. Its potential energy relative to

the ground is

A) 8 J.

B) 20 J.

C) 60 J.

D) 80 J.

E) none of the above

Answer: D

16) A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its

height?

A) 1 m

B) 2 m

C) 3 m

D) 4 m

E) none of the above

Answer: B

17) The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on

the

A) initial height of the ram.

B) initial potential energy of the ram.

C) distance the ram falls.

D) all of the above

Answer: D

18) Which has greater kinetic energy, a car traveling at 30 km/h or another car of half the mass

traveling at 60 km/h?

A) the 30-km/h car

B) the 60-km/h car

C) both have the same kinetic energy

Answer: B

19) A shopping cart moves with a kinetic energy of 40 J. If it moves at twice the speed, its

kinetic energy is

A) 40 J.

B) 80 J.

C) 160 J.

D) not enough information

Answer: C

20) A dog and a mouse run along a road with the same kinetic energy. The faster runner is the

A) dog.

B) mouse.

C) both run at the same speed.

D) not enough information

Answer: B

21) You do work on an object when you lift it against gravity. How does this work relate to

gravitational potential energy? If the lifted body is dropped, what becomes of this energy?

Answer: The work you do on the lifted body may be stored as gravitational potential energy.

Then the force × the distance = the weight × height. If the lifted object is dropped, this energy

transforms to motion energy–kinetic energy. The kinetic energy it possesses as it returns to its

initial position equals the gravitational potential energy at its highest point, which equals the

initial work done.

22) Discuss how energy conservation applies to a swinging pendulum. Where is potential energy

the most? The least? Where is kinetic energy the most? The least? Where is the pendulum bob

moving fastest? Slowest?

Answer: The swinging pendulum has the most gravitational potential energy at the top of its

swing. It has the most kinetic energy at the bottom of its swing, where its potential energy is at a

minimum. Halfway down, it has half kinetic and half potential energy. Everywhere along the

swing the sum of the kinetic and potential energies is the same. When air resistance and friction

are taken into account, kinetic energy is transferred from the pendulum to the surrounding space

as thermal energy.

23) Can an object have mechanical energy without having momentum? Momentum without

having mechanical energy? Explain.

Answer: An object can have potential energy without moving, which means it can have

mechanical energy without having momentum. But if its mechanical energy is kinetic, then it

also has momentum. Any object with momentum also has kinetic energy. (All objects also have

"energy of being" or mass energy, E = mc2.)

24) Why does the force of gravity do no work on a bowling ball rolling along a bowling alley

lane?

Answer: Work is done on an object only when a force, or some component of a force, acts in the

direction of motion of the object. In the case of the bowling ball, the force of gravity is

perpendicular to the motion with no component parallel to the lane. (We will see later that, for

the same reason, the force of gravity does no work on satellites in circular orbit.)

25) Suppose you are at the edge of a cliff and you throw one ball downward and another ball

upward at the same speed. Which will hit the ground faster? Does direction of the thrown ball

make a difference? Explain.

Answer: According to the conservation of energy, for the same initial speed the initial kinetic

energy is the same–regardless of the direction the ball is thrown. Thrown from the same height

means that its initial potential energy is the same, so its total energy is the same for all directions,

all of which is converted to kinetic energy when the ball hits the ground below. This means the

ball will have the same speed in all cases. How about that!

26) Give two explanations of why a cannonball fired from a long-barrel cannon will have a

greater velocity than from a shorter cannon.

Answer: In terms of impulse-momentum, the longer barrel means the time during which the

exploding powder pushes on the cannonball is longer. This means more impulse, which in turn

means more gain in momentum, and greater velocity. In terms of work-energy, the longer barrel

means a longer distance for the force to act, which means more gain in kinetic energy, and

greater velocity.

3.5 Work-Energy Theorem

1) When a non-hybrid car brakes to a stop its kinetic energy transforms to

A) stopping energy.

B) potential energy.

C) energy of motion.

D) energy of rest.

E) heat.

Answer: E

2) No work is done by gravity on a bowling ball that rolls along a bowling alley because

A) no force acts on the ball.

B) no distance is covered by the ball.

C) the force on the ball is at right angles to the ball's motion.

D) no potential energy converts to kinetic energy.

E) its kinetic energy may vary.

Answer: C

3) A car moves 4 times as fast as another identical car. Compared with the slower car, the faster

car has

A) 4 times the kinetic energy.

B) 8 times the kinetic energy.

C) 12 times the kinetic energy.

D) 16 times the kinetic energy.

Answer: D

4) A ball is projected into the air with 900 J of kinetic energy that is transformed to potential

energy at the top of its trajectory. When it returns to its original level after encountering air

resistance, its kinetic energy is

A) less than 900 J.

B) more than 900 J.

C) 900 J.

D) not enough information

Answer: A

5) A car moving at 50 km/h skids 20 m with locked brakes. How far will it skid if its initial speed

is 150 km/h?

A) 20 m

B) 60 m

C) 90 m

D) 120 m

E) 180 m

Answer: E

6) Which requires more work on the brakes of a car?

A) slowing down from 100 km/h to 70 km/h

B) slowing down from 70 km/h to a stop

C) equal amounts of work for either

Answer: A

7) A car that travels twice as fast as another car when braking to a stop will skid

A) twice as far.

B) four times as far.

C) depends on the mass of the cars

Answer: B

8) Two identical arrows, one with twice the speed of the other are fired into a bale of hay. The

faster arrow will penetrate the bale

A) the same distance as the slower arrow.

B) twice as far as the slower arrow.

C) four times as far as the slower arrow.

D) more than four times as far as the slower arrow.

E) none of the above

Answer: C

9) A boulder is dropped onto mud and plows into it a certain distance. If it hits with three times

as much speed, the distance it plows into the mud will likely be

A) the same distance.

B) twice as deep.

C) three times as deep.

D) more than three times as deep.

Answer: D

3.6 Conservation of Energy

1) A hydraulic press properly arranged, like a simple lever, is capable of multiplying energy

input.

A) true

B) sometimes true

C) false

Answer: C

2) Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack

vertically 4 m?

A) lifting the 50-kg sack

B) lifting the 25-kg sack

C) both require the same amount of work

Answer: C

3) In raising a 5000-N piano with a pulley system, for every 1 m of rope pulled down, the piano

rises 0.1 m. Ideally, this means the force needed to lift the piano is

A) 50 N.

B) 500 N.

C) 5000 N.

D) not enough information

Answer: B

4) Strictly speaking, if any electrical device in an automobile is turned on (such as an air

conditioner, headlights, or radio), more fuel is consumed by the engine. This statement is

A) true.

B) true only if the engine is running.

C) always false

D) sometimes true, sometimes false

Answer: A

5) A diver who weighs 500 N steps off a diving board 10 m above the water hits the water with

kinetic energy of

A) 10 J.

B) 500 J.

C) 510 J.

D) 5000 J.

E) more than 5000 J.

Answer: D

6) When the input piston of a hydraulic press is depressed 20 cm, the output piston is observed to

move 1 cm. An input force of 1 N can raise no more than

A) 1 N.

B) 10 N.

C) 20 N.

D) 21 N.

Answer: C

7) A 2500-N pile driver ram falls 10 m and drives a post 0.1 m into the ground. The average

force on the post is

A) 2500 N.

B) 25,000 N.

C) 250,000 N.

D) 2,500,000 N.

Answer: C

8) A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The

amount of energy converted to heat is about

A) 0.5 J.

B) 1.0 J.

C) 1.5 J.

D) 2.0 J.

E) more than 2.0 J.

Answer: E

9) A person on the edge of a roof throws a piece of tile downward that strikes the ground with

100 J of kinetic energy. Another identical tile is thrown upward with the same initial speed, and

this too falls to the ground. Neglecting air resistance, the second tile hits the ground with a

kinetic energy of

A) less than 100 J.

B) 100 J.

C) 200 J.

D) more than 200 J.

E) none of the above

Answer: B

10) Compared to a recoiling rifle, the bullet that is fired has a greater

A) momentum.

B) kinetic energy.

C) none of the above

Answer: B

11) A golf ball is thrown at and bounces backward from a massive bowling ball that is initially at

rest. After the collision, compared to the golf ball, the bowling ball has more

A) momentum, but less kinetic energy.

B) kinetic energy, but less momentum.

C) momentum and more kinetic energy.

D) less momentum and less kinetic energy.

E) not enough information

Answer: A

12) A popular swinging-balls apparatus (Newton's cradle) consists of a series of identical elastic

balls suspended by strings so they barely touch each other. When two balls are pulled away from

one end and released, they strike the row of balls and two balls pop out from the other end. If

instead, one ball popped out with twice the speed, this would be a violation of conservation of

A) momentum.

B) energy.

C) both

D) none of the above

Answer: B

13) A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The

momentum of the two pieces of taffy stuck together after the collision is the same as it was

before the collision. Kinetic energy is a different story, for part of it turns into heat. What

percentage of the kinetic energy converts into heat?

A) 0%

B) 25%

C) 50%

D) 75%

E) not enough information

Answer: C

14) A sandbag in outer space moves at 3 m/s when it collides and sticks to a half-as-massive

sandbag initially at rest. Compared with the kinetic energy of the moving sandbag before

collision, the kinetic energy of the coupled sandbags after collision is

A) one-third.

B) two-thirds.

C) three-quarters.

D) not enough information

Answer: B

3.7 Power

1) If you do work on an object in half the time, your power output is

A) half.

B) the same.

C) twice.

Answer: C

2) Exert 1 N for a distance of 1 m in 1 s and you deliver a power of

A) 1 W.

B) 2 W.

C) 1/3 W.

D) 3 W.

E) none of the above

Answer: A

3) Exert 100 J in 50 s and your power output is

A) 1/4 W.

B) 1/2 W.

C) 2 W.

D) 4 W.

E) more than 4 W.

Answer: C

4) Using 1000 J of work, a toy elevator is raised from the ground floor to the second floor in 20

s. How much power does the elevator use?

A) 20 W

B) 50 W

C) 100 W

D) 1000 W

E) 20,000 W

Answer: B

5) A 50-kg sack is lifted 2 m in the same time as a 25-kg sack is lifted 4 m. The power expended

in raising the 50-kg sack compared to the power used to lift the 25-kg sack is

A) twice as much.

B) half as much.

C) the same.

Answer: C

6) The power expended for a barbell raised 2.0 m in 2 s is

A) 1 W.

B) 4 W.

C) 8 W.

D) not enough information

Answer: D

3.8 Machines

1) A simple machine CANNOT multiply

A) force.

B) distance.

C) energy.

D) none of the above

Answer: C

2) The most underlying feature of machines is

A) the conservation of energy.

B) that energy input always equals energy output.

C) that power input always equals power output.

D) all of the above

E) none of the above

Answer: A

3) When a simple machine multiplies force, it decreases

A) potential energy.

B) distance moved.

C) both

D) neither

Answer: B

4) Lifting a 100-N load with 50 N of force lifts it

A) half as high.

B) as high.

C) twice as high

Answer: A

3.9 Efficiency

1) A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the

machine is

A) 10%.

B) 50%.

C) 90%.

D) 110%.

E) none of the above

Answer: A

2) A jack system will increase the potential energy of a heavy load by no more than 1000 J with

a work input of 2000 J. The efficiency of the jack system is at most

A) 10%.

B) 20%.

C) 50%.

D) 80%.

E) not enough information

Answer: C

3) If a power plant is 30% efficient, and the transmission system that delivers power to

consumers is 60% efficient, then the overall efficiency is

A) 90%.

B) 60%.

C) 30%.

D) 18%.

E) none of the above

Answer: D

4) Suppose a miracle car has a 100% efficient engine and burns fuel having an energy content of

40 MJ/L. If the air resistance and overall frictional forces on this car traveling at highway speeds

is 1000 N, what is the overall limit in distance per liter driven on the highway?

A) 30 km

B) 40 km

C) 50 km

D) more than 50 km

E) not enough information

Answer: B

5) A common car engine is 20% efficient. When cruising, the car encounters an average

retarding force of 1000 N. If the energy content of gasoline is 40 MJ/L, how many kilometers per

liter does the car achieve?

A) 14 km/L

B) 12 km/L

C) 10 km/L

D) 8 km/L

E) none of the above

Answer: D

3.10 Sources of Energy

1) Which of these forms of energy is NOT renewable?

A) wind power

B) solar power

C) fossil fuel power

D) photovoltaic power

Answer: C

2) The most energy per unit mass can be extracted from

A) coal.

B) petroleum.

C) natural gas.

D) uranium.

Answer: D

3) The source of Earth's internal energy involves

A) kinetic energy.

B) potential energy.

C) radioactivity.

D) the Sun.

Answer: C

4) The ultimate source of energy from fossil fuels is the

A) Sun.

B) radioactivity in Earth's interior.

C) photosynthesis process.

D) natural processes in Earth's interior.

Answer: A

Test Bank for Conceptual Physical Science

Paul Hewitt, John Suchocki, Leslie Hewitt

9780321752932, 9780134060491