Chapter 6

Momentum

When a farmer throws a 3-kg pumpkin at a speed of 4 m/s onto a compost pile, the pumpkin’s momentum just before

hitting the pile is

a. 0 kg•m/s.b. 5 kg•m/s.c. 7 kg•m/s.d. 12 kg•m/s.

When a farmer throws a 3-kg pumpkin at a speed of 4 m/s onto a compost pile, the pumpkin’s momentum just before

hitting the pile is

a. 0 kg•m/s.b. 5 kg•m/s.c. 7 kg•m/s.d. 12 kg•m/s.

Compared with the momentum of a 200-lb man running 10 mi/h, the

momentum of a 2000-lb car moving 1 mph is

a. zero.b. the same.c. greater.d. less.

Compared with the momentum of a 200-lb man running 10 mi/h, the

momentum of a 2000-lb car moving 1 mph is

a. zero.b. the same.c. greater.d. less.

A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels at the

same speed on the Moon, its momentum is

a. the same.b. less.c. more.d. zero.

A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels at the

same speed on the Moon, its momentum is

a. the same.b. less.c. more.d. zero.

When both the force and time of contact are doubled, the impulse on an

object isa. unchanged.b. doubled. c. quadrupled.d. decreased.

When both the force and time of contact are doubled, the impulse on an

object isa. unchanged.b. doubled. c. quadrupled.d. decreased.

Your friend says that impulse equals momentum. Your friend’s statement is not correct, and the missing word is

a. work.b. acceleration.c. speed or velocity.d. change.

Your friend says that impulse equals momentum. Your friend’s statement is not correct, and the missing word is

a. work.b. acceleration.c. speed or velocity.d. change.

If a car comes to a full stop when hitting a haystack and when hitting a

stone wall, the change in momentum is greater for hitting the

a. haystack.b. stone wall.c. Same momentum change in both cases.d. None of the above.

If a car comes to a full stop when hitting a haystack and when hitting a

stone wall, the change in momentum is greater for hitting the

a. haystack.b. stone wall.c. Same momentum change in both cases.d. None of the above.

Explanation: Although the change in momentum is the same for both cases, the forces involved are quite different!

A 1-kg ball has the same speed as a 10-kg ball. Compared with the 1-kg

ball, the 10-kg ball hasa. less momentum.b. the same momentum.c. 10 times as much momentum.d. 100 times as much momentum.

A 1-kg ball has the same speed as a 10-kg ball. Compared with the 1-kg

ball, the 10-kg ball hasa. less momentum.b. the same momentum.c. 10 times as much momentum.d. 100 times as much momentum.

Explanation: Let the definition mv guide your thinking.

Which of the following equations most directly illustrates the safety value

of automobile airbags?a. F = ma.b. Ft = ∆(mv).c. d = 1/2 at2.d. v = gt.

Which of the following equations most directly illustrates the safety value

of automobile airbags?a. F = ma.b. Ft = ∆(mv).c. d = 1/2 at2.d. v = gt.

A ball is tossed into a bale of hay and comes to a stop. If instead, it comes to a stop when hitting a sticky solid wall, the

impulse needed to stop it is

a. less.b. the same.c. more.d. zero.

A ball is tossed into a bale of hay and comes to a stop. If instead, it comes to a stop when hitting a sticky solid wall, the

impulse needed to stop it is

a. less.b. the same.c. more.d. zero.

When a falling object bounces as it hits the ground

a. the impulse on it is greater than for stopping it.b. its change in momentum is greater than for

stopping.c. Both of these.d. None of these.

When a falling object bounces as it hits the ground

a. the impulse on it is greater than for stopping it.b. its change in momentum is greater than for

stopping.c. Both of these.d. None of these.

When you jump from an elevated position to the ground below, the force

you experience when landing does NOT depend on

a. the jumping height.b. the softness or hardness of the ground.c. how much you bend your knees.d. your attitude about jumping.

When you jump from an elevated position to the ground below, the force

you experience when landing does NOT depend on

a. the jumping height.b. the softness or hardness of the ground.c. how much you bend your knees.d. your attitude about jumping.

Nets used to catch falling boulders on the side of rocky hillside roadways are

more effective than rigid fences because their breakage is reduced by

a. less impulse of falling rocks.b. less momentum of falling rocks.c. more time to change the momentum of falling

rocks.d. less time to change the momentum of falling

rocks.

Nets used to catch falling boulders on the side of rocky hillside roadways are

more effective than rigid fences because their breakage is reduced by

a. less impulse of falling rocks.b. less momentum of falling rocks.c. more time to change the momentum of falling

rocks.d. less time to change the momentum of falling

rocks.

Standing still on a skateboard, you catch a ball tossed horizontally to you. The mass of the ball is one-tenth your mass. Compared with the

speed of the caught ball, the speed that both you and the caught ball acquire is

a. the same.b. one-tenth as much.c. 10 times as much.d. 100 times as much.

Standing still on a skateboard, you catch a ball tossed horizontally to you. The mass of the ball is one-tenth your mass. Compared with the

speed of the caught ball, the speed that both you and the caught ball acquire is

a. the same.b. one-tenth as much.c. 10 times as much.d. 100 times as much.

When Jake tosses a ball while standing still on his skateboard, he and his skateboard recoil. If he goes through the motions of tossing the ball, but doesn’t toss it, his net recoil will ideally be

a. the same as if he threw the ball.b. almost as much as if he threw the ball.c. very small.d. zero.

When Jake tosses a ball while standing still on his skateboard, he and his skateboard recoil. If he goes through the motions of tossing the ball, but doesn’t toss it, his net recoil will ideally be

a. the same as if he threw the ball.b. almost as much as if he threw the ball.c. very small.d. zero.

When you say momentum is conserved, you mean that

a. when an impulse acts on an object, its momentum will change.

b. momentum can be stored.c. when external impulses don’t occur, a system’s

momentum remains the same before and after an interaction.

d. when two objects collide, the mass and velocity of each object will not change.

When you say momentum is conserved, you mean that

a. when an impulse acts on an object, its momentum will change.

b. momentum can be stored.c. when external impulses don’t occur, a system’s

momentum remains the same before and after an interaction.

d. when two objects collide, the mass and velocity of each object will not change.

In the absence of external forces, momentum is conserved in

a. an elastic collision.b. an inelastic collision.c. either an elastic or an inelastic collision.d. neither an elastic nor an inelastic collision.

In the absence of external forces, momentum is conserved in

a. an elastic collision.b. an inelastic collision.c. either an elastic or an inelastic collision.d. neither an elastic nor an inelastic collision.

A big fish coasts up to and swallows a small fish at rest. Right after lunch,

the speed of the big fish isa. the same as before. b. less than before. c. more than before.d. zero.

A big fish coasts up to and swallows a small fish at rest. Right after lunch,

the speed of the big fish isa. the same as before. b. less than before. c. more than before.d. zero.

A big fish swims up on and swallows a small fish at rest. Right after lunch,

the momentum of the big fish isa. the same as before.b. less than before. c. more than before.d. zero.

A big fish swims up on and swallows a small fish at rest. Right after lunch,

the momentum of the big fish isa. the same as before.b. less than before. c. more than before.d. zero.

A piece of clay moving with one unit of momentum strikes and sticks to a heavy bowling ball initially at rest. After the clay sticks, both the clay and ball ideally move

with a combined momentum of

a. a little less than one unit.b. one unit.c. more than one unit.d. much less than one unit.

a. a little less than one unit.b. one unit.c. more than one unit.d. much less than one unit.

Explanation: Straight logic; the momentum before the interaction was one unit, and in the absence of external forces remains one unit after the interaction.

A piece of clay moving with one unit of momentum strikes and sticks to a heavy bowling ball initially at rest. After the clay sticks, both the clay and ball ideally move

with a combined momentum of

A pair of spiral galaxies collide and merge to form one larger elliptical galaxy. Astronomers assume that the momentum

of the new elliptical galaxy is

a. equal to the sum of the momenta of two spiral galaxies.

b. equal to the difference in momenta of the two spiral galaxies.

c. the same as the momentum of the more massive spiral galaxy.

d. zero.

A pair of spiral galaxies collide and merge to form one larger elliptical galaxy. Astronomers assume that the momentum

of the new elliptical galaxy is

a. equal to the sum of the momenta of two spiral galaxies.

b. equal to the difference in momenta of the two spiral galaxies.

c. the same as the momentum of the more massive spiral galaxy.

d. zero.