enriched mo practice

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Multiple Choice
Identify the choice that best completes the statement or answers the question.

The momentum of an object is defined as the object's

a.	mass times its velocity.
b.	force times the time interval.
c.	force times its acceleration.
d.	mass times it acceleration.
e.	velocity times the time interval.

Which has more momentum, a large truck moving at 30 miles per hour or a small truck moving at 30 miles per hour?

a.	Both have the same momentum.
b.	The small truck
c.	The large truck

Compared to a sports car moving at 30 miles per hour, the same sports car moving at

miles per hour has

a.	twice as much momentum.
b.	four times as much momentum.
c.	the same momentum.

The momentum change of an object is equal to the

a.	impulse acting on it.
b.	velocity change of the object.
c.	force acting on it.
d.	force acting on it times its velocity.
e.	object's mass times the force acting on it.

In order to increase the final momentum of a golf ball, we could

a.	increase the force acting on it.
b.	follow through when hitting the ball.
c.	increase the time of contact with the ball.
d.	swing as hard as possible.
e.	all of the above

The reason padded dashboards are used in cars is that they

a.	look nice and feel good.
b.	decrease the impulse in a collision.
c.	increase the force of impact in a collision.
d.	decrease the momentum of a collision.
e.	increase the time of impact in a collision.

A table tennis ball launcher is fired. Compared to the force on the ball, the force on the launcher is

a.	larger.
b.	the same.
c.	smaller.

Momentum of a system is conserved only when

a.	there are no internal forces acting on the system.
b.	the system is not moving.
c.	there are no forces acting on the system.
d.	there is no net external force acting on the system.
e.	the system has zero momentum.

Suppose a girl is standing on a pond where there is no friction between her feet and the ice. In order to get off the ice, she can

a.	bend over touching the ice in front of her and then bring her feet to her hands.
b.	walk very slowly on tiptoe.
c.	get on her hands and knees and crawl off the ice.
d.	throw something in the direction opposite to the way she wants to go.
e.	all of the above will work

10.

Which of the following has the largest momentum?

a.	A large truck parked in a parking lot
b.	A tightrope walker crossing Niagara Falls
c.	The science building at your school
d.	A pickup truck traveling down the highway
e.	A dog running down the street

11.

A freight train rolls along a track with considerable momentum. If it were to roll at the same speed but had twice as much mass, its momentum would be

a.	zero.
b.	unchanged.
c.	quadrupled.
d.	doubled.

12.

A cannon recoils from launching a cannonball. The speed of the cannon's recoil is small because the

a.	impulse on the cannon is less than the impulse on the cannonball.
b.	cannon has far more mass than the cannonball.
c.	momentum of the cannon is unchanged.
d.	force against the cannon is relatively small.
e.	none of the above

13.

Suppose a cannon is made of a strong but very light material. Suppose also that the cannonball is more massive than the cannon itself. For such a system

a.	conservation of momentum would not hold.
b.	conservation of energy would not hold.
c.	the target would be a safer place than where the operator is located.
d.	the force on the cannonball would be greater than the force on the cannon.
e.	recoil problems would be lessened.

14.

Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher

a.	acceleration.
b.	momentum.
c.	speed.
d.	all of the above
e.	none of the above

15.

In order to catch a ball, a baseball player moves his or her hand backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because

a.	the time of impact is decreased.
b.	the time of impact is increased.
c.	the velocity of the hand is reduced.
d.	the momentum of impact is reduced.
e.	none of the above

16.

A car traveling along the highway needs a certain amount of force exerted on it to stop. More stopping force may be required when the car has

a.	less stopping distance.
b.	more momentum.
c.	more mass.
d.	all of the above
e.	none of the above

17.

Recoil is noticeable if you throw a heavy ball while standing on roller skates. If instead you go through the motions of throwing the ball but hold onto it, your net recoil velocity will be

a.	small but noticeable.
b.	the same as before.
c.	zero.

18.

A karate expert executes a swift blow and splits a cement block with her bare hand.

a.	The forces on both the block and the expert's hand have the same magnitude.
b.	The times of impact on both the block and the expert's hand are the same.
c.	The impulses on both the block and the expert's hand have the same magnitude.
d.	all of the above
e.	none of the above

19.

A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collision is

a.	zero.
b.	one half as large.
c.	the same.
d.	twice as large.
e.	More information is needed to say.

20.

Two gliders having the same mass and speed move toward each other on an air track and stick together. After the collision, the velocity of the gliders is

a.	twice the original velocity.
b.	one half the original velocity.
c.	zero.
d.	the same as the original velocity.
e.	There is not enough information to say.

21.

A piece of putty moving with 2 units of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both are set in motion with a combined momentum that is

a.	less than 2 units.
b.	2 units.
c.	more than 2 units.
d.	There is not enough information to say.

22.

If all people, animals, trains and trucks all over the world began to walk or run towards the east, then

a.	Earth would spin a bit slower.
b.	Earth's spin would not be affected at all.
c.	Earth would spin a bit faster.

23.

Suppose an astronaut in outer space wishes to toss a ball against a very massive and perfectly elastic concrete wall and catch it as it bounces back. If the ball is as massive as the astronaut, then

a.	the astronaut's time between catches will decrease as the game progresses.
b.	the astronaut will never catch the first bounce.
c.	the astronaut will catch one bounce only.
d.	none of the above

24.

A table tennis ball moving forward with 5 units of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of

a.	less than 5 units.
b.	5 units.
c.	more than 5 units.
d.	not enough information.

25.

Superman is at rest in space when he throws an asteroid that has more mass than he does. Which moves faster, Superman or the asteroid?

a.	Superman
b.	The asteroid
c.	They both move at the same speed.

26.

While roller-skating, Granny collides with her tiny grandson Ambrose who is at rest. Ignoring any friction effects, Ambrose's speed after the collision will be greatest when

a.	Granny catches him and they both move together.
b.	he and Granny make a bouncing collision, each going in opposite directions.

27.

A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives the greater impulse is the

a.	limousine.
b.	small economy car.
c.	neither A nor B (same for each).

28.

A 4.0-kg ball has a momentum of 20.0 kg·m/s. What is the ball's speed?

a.	0.2 m/s
b.	5.0 m/s
c.	20.0 m/s
d.	80.0 m/s
e.	none of the above

29.

A ball is moving at 6.0 m/s and has a momentum of 24.0 kg·m/s. What is the ball's mass?

a.	0.3 kg
b.	4.0 kg
c.	24.0 kg
d.	144.0 kg
e.	none of the above

30.

A 5.0-kg chunk of putty moving at 10.0 m/s collides with and sticks to a 7.0-kg bowling ball that is initially at rest. The bowling ball with its putty passenger will then be set in motion with a momentum of

a.	0 kg·m/s.
b.	2.0 kg·m/s.
c.	15.0 kg·m/s.
d.	50.0 kg·m/s.
e.	more than 50.0 kg·m/s.

31.

If the momentum of an object changes and its mass remains constant,

a.	it is accelerating (or decelerating).
b.	there is a force acting on it.
c.	its velocity is changing.
d.	all of the above
e.	none of the above

32.

A table tennis ball launcher is fired. Compared to the impulse on the ball, the impulse on the launcher is

a.	smaller.
b.	larger.
c.	the same.

33.

A collision is considered elastic if

a.	there is no lasting deformation.
b.	the objects don’t stick together.
c.	the objects that collide don't get warmer.
d.	after the collision, the objects have the same shape as before the collision.
e.	all of the above

34.

A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon

a.	if the mass of the cannonball equals the mass of the cannon.
b.	because momentum is conserved.
c.	because velocity is conserved.
d.	because both velocity and momentum are conserved.
e.	none of the above

35.

The force of an apple hitting the ground depends upon

a.	the speed of the apple just before it hits.
b.	the time of impact with the ground.
c.	whether or not the apple bounces.
d.	air resistance on the apple as it falls.
e.	all of the above

36.

When you jump off a step, you usually bend your knees as you reach the ground. By doing this, the time of the impact is about 10 times more what it would be in a stiff-legged landing, and the average force on your body is reduced by

a.	less than 10 times.
b.	about 10 times.
c.	more than 10 times.

37.

A 1-N apple falls to the ground. The apple hits the ground with an impact force of

a.	1 N.
b.	2 N.
c.	4 N.
d.	9.8 N.
e.	Not enough information to say

38.

The force that accelerates a rocket into outer space is exerted on the rocket by

a.	the exhaust gases.
b.	Earth's gravity.
c.	atmospheric pressure.
d.	rocket's wings.
e.	none of the above

39.

A cannonball shot from a long-barrel cannon travels faster than one shot from a short-barrel cannon because the cannonball receives a greater

a.	force.
b.	impulse.
c.	both A and B
d.	neither A nor B

40.

A 2-kg ball is thrown at 3 m/s. What is the ball's momentum?

a.	2 kg·m/s
b.	3 kg·m/s
c.	6 kg·m/s
d.	9 kg·m/s
e.	none of the above

True/False
Indicate whether the statement is true or false.

41.

Momentum is defined as an object's mass times its velocity.

42.

If the net external force acting on a system is zero, then the total momentum of the system is zero.

43.

When two objects collide and completely bounce apart with no lasting deformation or generation of heat, the collision is said to be elastic.

44.

When two objects collide and stick together, the collision is said to be inelastic.

45.

Impulses are normally smaller when bouncing takes place.

46.

Automobile dashboards that are padded lengthen the time of impact in case of a collision.

47.

Momentum is a scalar quantity.

48.

Impulse is defined as the force exerted on an object times the time it lasts.

49.

Perfectly elastic collisions between large objects are uncommon in the everyday world.

50.

When a baseball player follows through in hitting the ball, the contact time with the ball is longer.

51.

If a net force acts on a system, the system's momentum will change.

Essay

52.

In terms of momentum change, explain why it is best to "give" when catching a baseball. Provide other examples of situations in which you want to lengthen the impact time in a collision.

53.

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.

54.

A boy fires a table tennis launcher. Briefly describe the forces and impulses on the launcher and the ball. Which has more momentum? Which is moving faster? Explain.

55.

What does it mean to say that momentum is conserved? Give at least two examples where momentum is conserved in a collision.

56.

A railroad diesel engine coasting at 12 km/h runs into a stationary flatcar. The diesel weighs 5 times as much as the flatcar. Assuming the cars couple together, how fast are they moving after the collision?

Problem

57.

What is the average momentum of a 50-kg skateboarder who covers 400 m in 50 s?

58.

A cement truck of mass 16,000 kg moving at 15 m/s slams into a cement wall and comes to a halt. What is the force of impact on the truck?

59.

A 10-kg cement block moving horizontally at 6 m/s plows into a bank of sand and comes to a stop in 2 s. What is the average impact force on the bank?

60.

An 8-kg blob of clay moving horizontally at 2 m/s hits a 3-kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision?

61.

A 40-kg football player leaps through the air to collide with and tackle a 50-kg player heading toward him, also in the air. If the 40-kg player is heading to the right at 9 m/s and the 50-kg player is heading toward the left at 2 m/s, what is the speed and direction of the tangled players?

62.

A 5-kg blob of clay moving horizontally at 4 m/s has a head-on collision with a 4-kg blob of clay that moves toward it at 2 m/s. What is the speed of the two blobs stuck together immediately after the collision?

63.

A 50-kg cart moving at 100 km/h collides head-on with an approaching 50-kg cart moving at 10 km/h (in the opposite direction). If the two carts stick together, what will be their speed?

64.

A 30-kg girl and a 50-kg boy face each other on friction-free roller skates. The girl pushes the boy, who moves away at a speed of 3 m/s. What is the girl's speed?

65.

Assume that a 15-kg ball moving at 8 m/s strikes a wall perpendicularly and rebounds elastically at the same speed. What is the amount of impulse given to the wall?

66.

A 10-kg bowling ball moving at 4 m/s bounces off a spring at about the same speed that it had before bouncing. What is the change in momentum of the bowling ball?

67.

A loaded freight car has 5 times as much mass as an empty freight car. If the loaded car coasts at 5 m/s and collides with and attaches to the empty car at rest, what will be the speed of both cars after collision?

68.

A 70-kg free-floating astronaut fires 0.10-kg of gas at a speed of 30 m/s from her propulsion pistol. What is the astronaut's recoil speed?