Deck 7: Momentum and Impulse

Question 1

Suppose you are out on a frozen lake, where there is no friction. Which of the following would start you moving towards the shore?

A) Shouting at someone on the shore.
B) Removing a shoe and throwing it away from the shore.
C) Removing a shoe and throwing it towards the shore.
D) None of these would work.

Answer 1

Removing a shoe and throwing it away from the shore.

Question 2

Which of the following mathematical expressions should be used to calculate the momentum of an auto?

A) weight $\times$ speed
B) mass $\times$ acceleration
C) weight $\times$ force
D) mass $\times$ velocity

Answer 2

mass $\times$ velocity

Question 3

A quantity which is conserved in the collision of a car and a truck is

A) kinetic energy.
B) nervous energy.
C) momentum of the car.
D) momentum of the truck.
E) total momentum.

Answer 3

total momentum.

Question 4

A gun is made of a super-low-weight but strong material. The bullet for the gun is more massive than the gun itself. For such a gun

A) recoil problems would be lessened.
B) the gun, if unsupported, would have a recoil velocity higher than the bullet velocity.
C) conservation of momentum is not satisfied.
D) the bullet would go faster with less powder.

Question 5

A fire fighting vehicle of mass 12,000 kg is at rest but free to roll with no resistance. If you push it forward with a force of 500 N, the momentum at the end of 10 s of pushing will be

A) 5000 kg m/s.
B) 20,000 kg N/s.
C) 0.416 m/s.
D) zero.

Question 6

A child runs at 3.0 m/s and jumps onto a sled, initially at rest. If the child's mass is 36 kg, and if the child and sled slide off together at 2.0 m/s after the collision, the sled's mass is

A) 12 kg.
B) 18 kg.
C) 36 kg.
D) 48 kg.

Question 7

In a head-on automobile collision, a person's momentum could be reduced from 2000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is

A) 20,000 N.
B) 2,000 N.
C) 200 N.
D) This can't be answered without knowing the person's mass.

Question 8

The purpose of an air bag in an auto is to

A) decrease the force applied to you during a collision.
B) reduce the impulse on you during a collision.
C) make your momentum change occur over a shorter time during a collision.
D) reduce your speed just before a collision.

Question 9

In attempting to pull a 1500-kg car out of a ditch, Arnold exerts a force of 300 N for three seconds, Bob exerts a force of 500 N for two seconds, and Cecil exerts a force of 200 N for four seconds. Who provided the greatest impulse?

A) Arnold
B) Bob
C) Cecil

Question 10

A ping-pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision?

A) The bowling ball.
B) The ping-pong ball.
C) Neither, both experience forces of the same size.
D) It's impossible to tell from this data.

Question 11

Object A moving due east collides with object B moving due west. After the collision, A is moving 20 $\degree$ north of due east. What must be true of B after the collision?

A) B must be moving 20 $\degree$ south of due east.
B) B must be moving 20 $\degree$ south of due west.
C) At least part of B's velocity must be toward the south.
D) At least part of B's velocity must be toward the west.
E) None of these are true.

Question 12

One form of the proper metric unit for momentum is

A) Joule.
B) Kg·m.
C) Kg·m/s².
D) N·sec.

Question 13

Two people sit face to face on nice skateboards that are free to roll without friction. They push each other with a force of 40 N and move apart. Person X, whose mass (including the skateboard) is 50 kg, moves to the left at 3 m/s. Person Z, whose mass (including the skateboard) is 60 kg,

A) moves to the right at 2.5 m/s.
B) moves to the right at 1 m/s.
C) moves to the right at 4 m/s.
D) moves to the right at 10 m/s.

Question 14

An 80-kg football player travels to the right at 8 m/s and a 120-kg player on the opposite team travels to the left at 4.0 m/s. The total momentum is

A) 240 kg m/s to the left.
B) 160 kg m/s to the right.
C) zero.
D) 160 kg m/s to the left.
E) 1120 kg m/s to the right.

Question 15

When a baseball bat hits the ball, the impulse delivered to the ball is increased by

A) "follow through" on the swing, which increases contact time.
B) rapidly stopping the bat after impact.
C) letting the bat recoil upon impact.
D) The impulse cannot be changed.

Question 16

The average force required to accelerate a 0.20-kg ball from rest to 30 m/s in 0.002 s is

A) 75,000 N.
B) 15,000 N.
C) 3,000 N.
D) 0.003 N

Question 17

A bowling ball, moving to the east at a speed of 1.4 m/s, collides head-on with a stationary beach ball of the same diameter but less than one twentieth the mass. After the collision, the beach ball moves with a speed of 1.6 m/s. Which of the following is then true?

A) The bowling ball has a velocity of slightly under 1.4 m/s, to the east.
B) The beach ball has more momentum than the bowling ball.
C) The bowling ball recoils to the west with nearly the same speed as before the collision.
D) The bowling ball and the beach ball have the same momentum after the collision.

Question 18

A tennis ball bounces off a brick wall. Which of the following is true?

A) The total momentum of the ball, wall, and Earth is conserved in this process.
B) The momentum of the ball is conserved in this process.
C) If the collision is elastic, then the ball's velocity does not change in this process.
D) None of these is true.

Question 19

A 30-kg child runs at 3.0 m/s and jumps onto a shopping cart and holds on for dear life. The cart has a mass of 20 kg. Assuming the child rides on the cart after the collision, the speed of the child and shopping cart just after the child jumps on is

A) zero.
B) 2.0 m/s.
C) 2.5 m/s.
D) 3.0 m/s.

Question 20

The momentum of a truck is increased by a factor of 2; its weight does not change. Thus,

A) its acceleration is doubled.
B) its speed doubled.
C) its speed increased by a factor of 4.
D) its kinetic energy doubled.

Question 21

A racquetball is dropped from a height of one meter. It bounces off the floor and rises to a height of 0.8 m. The collision with the floor was

A) an elastic collision.
B) a partially inelastic collision.
C) a perfectly inelastic collision.
D) impossible to tell without knowing the mass of the ball.

Question 22

A bullet of mass 0.010 kg and speed of 200 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. This process takes 0.02 second. The magnitude of the impulse delivered to the bullet by the block during this time is

A) zero.
B) 0.98 N.
C) 1.0 Ns.
D) 2.0 Ns.
E) 4.0 Ns.

Question 23

A box is moved 10 m across a smooth floor by a force F making a downward angle with the floor, so that there is effectively a 4 N force acting parallel to the floor in the direction of motion and a 3 N force acting perpendicular to the floor. The force F acts for 20 seconds. The impulse delivered to the box by the floor during this process has magnitude

A) 100 Ns.
B) 80 Ns.
C) 60 Ns.
D) zero.
E) Can't tell without knowing the weight of the box.

Question 24

If the speed of a car is tripled, the impulse required to stop the car changes by a factor of

A) 9.
B) 3.
C) 1.
D) 1/3.
E) 1/9.

Question 25

A bullet is fired into a wall and comes to rest. Considering only the bullet as the system we can say that

A) the total kinetic energy is conserved.
B) the momentum is conserved.
C) neither total kinetic energy nor momentum is conserved.
D) both total kinetic energy and momentum are conserved.

Question 26

Suppose two boys are trapped on the ice atop a frozen pond, and that the ice is completely frictionless. The boys are initially at rest, but they do have a baseball. They begin to play catch with the ball. Which of these is true?

A) The boys only move while the ball is in the air.
B) They will be stuck on the ice until rescued.
C) The more times they throw and catch the ball, the faster they will get to shore.
D) If after a few throws the ball is not caught and rolls away, the boys will be stuck on the ice.

Question 27

Collisions between which pairs of objects is likely to be most nearly elastic?

A) A steel ball and a cotton ball
B) Two steel balls
C) A steel ball and a baseball
D) Two baseballs

Question 28

Although Newton's second law, F = ma, is valid for collisions, it is difficult to use it generally in this form for collisions because

A) the acceleration is too small.
B) the force F is not constant.
C) the acceleration occurs during a time interval too short to measure easily.
D) the acceleration is too small and the force F is not constant.
E) the force F is not constant and the acceleration occurs during a time interval too short to measure easily.

Question 29

During a collision, which of these is an indication that the total momentum has changed?

A) Heat is generated.
B) Deformation occurs.
C) Sound is produced.
D) Heat is generated, deformation occurs, and sound is produced.
E) None of these are correct.

Question 30

Suppose a ball is dropped from shoulder height, falls, makes a perfectly elastic collision with the floor, and rebounds to shoulder height. Compare the magnitudes of the impulses delivered to the ball by gravity and by the floor during this entire motion.

A) The impulse delivered by the floor is half as large as the impulse delivered by gravity.
B) The impulse delivered by the floor is twice as large as the impulse delivered by gravity.
C) The two impulses have the same magnitude.
D) The floor delivers an upward impulse, but gravity does not deliver a total impulse.

Question 31

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force providing no impulse during the motion is

A) gravity.
B) friction.
C) the applied force.
D) none of these.

Question 32

Moving at a constant speed, an elevator lifts a 1000 N package 10 meters in 3 seconds. During this time, the impulse delivered to the package by the elevator floor is

A) 10,000 Ns up.
B) 3,000 Ns up.
C) 10,000 Nm up.
D) zero.

Question 33

A box is pushed eastward across a rough horizontal floor by a force acting parallel to the floor. A force providing an impulse directed westward on the body is

A) gravity.
B) the applied force.
C) friction.
D) normal reaction force of floor upward on body.
E) a fictitious force.

Question 34

If a force acts on an object, the impulse will be

A) zero if the force is applied perpendicular to the momentum object.
B) zero if the force is in the opposite direction of the velocity of the object.
C) zero if the speed of the object does not change.
D) nonzero in all situations.

Question 35

During a collision, which of these is an indication that the total kinetic energy has changed?

A) Heat is generated.
B) Deformation occurs.
C) Sound is produced.
D) Heat is generated, deformation occurs, and sound is produced.
E) None of these are correct.

Question 36

A car moving east collides with a truck moving north. The vehicles have the same speed but the truck has twice the mass of the car. If the vehicles stick together after the collision, what is the path followed by the vehicles after the collision?

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

Question 37

The principle that total momentum does not change during a brief collision is a result of

A) the definition of the kilogram.
B) the definition of the newton.
C) Newton's first law and Newton's second law.
D) Newton's first law and Newton's third law.
E) Newton's second law and Newton's third law.

Question 38

A 3 kg block, initially moving due east at 6 m/s, is acted upon by an impulse having magnitude 6 Ns and direction due west. The final velocity of the block is

A) 8 m/s east.
B) 4 m/s east.
C) 4 m/s west.
D) 8 m/s west.

Question 39

A painter of mass 80 kg climbs 3.0 m up a ladder. The painter has gained momentum in the amount of

A) 240 J.
B) 784 J.
C) 2352 J.
D) Can't say without knowing his velocity change (if any)

Question 40

A friend drops a package to you from a window 16 feet above where you first catch it. It drops an additional 3 feet as you bring it to a stop with a constant force. In order to calculate the force required, you need

A) the time it takes for you to stop the package.
B) the mass of the package.
C) no additional information.

Question 41

The impulse required to bring an auto to a stop is ordinarily provided by __________________ forces.

Question 42

A moving cue ball strikes another ball of equal mass that is initially at rest on the flat planar surface of the pool table. If the collision is elastic, the direction of the velocity of the cue ball after the collision will be __________________ to the direction of the velocity of the other ball.

Question 43

A toy car and a toy truck at rest have a compressed spring in between them. The truck has more mass than the car. The spring is released and the two cars move in opposite directions. Which of the following is true?

A) The magnitude of the truck's momentum is the same as the car's.
B) The magnitude of the truck's momentum is larger than the car's.
C) The magnitude of the truck's momentum is smaller than the car's.
D) It is not possible to tell which has more momentum without knowing the speeds.

Question 44

A force acts on an object for a time. If one eighth the force had acted for twice as long, the impulse would have been __________ as much as before.

Question 45

A robot spacecraft is sent to Mars to explore the Martian polar ice cap. Designers can surround it with a set of inflatable balloons that pop out like automobile air bags as soon as the spacecraft's re-entry parachute opens up. When the spacecraft lands, it will be able to roll for a few meters across the surface of Mars. The popout balloons have an advantage to the spacecraft, because

A) they cancel out the normal force of the surface of Mars.
B) they decrease the kinetic energy.
C) they increase the time of impact and lessen the stopping force.
D) the impulse that stops the spacecraft for landing is less with these balloons.

Question 46

If a single force acts on a moving object

A) the momentum of the object will change only if the force is in the same direction as the velocity of the object.
B) the momentum of the object must change.
C) the momentum of the object can only change magnitude, not direction.
D) the momentum of the object can only change direction, not magnitude.

Question 47

A big defensive lineman picks up a fumbled football and begins rumbling toward the end zone. His mass is 150 kg, and his velocity is 6.0 m/s, west. A brave wide receiver, whose mass is 90 kg, must stop that lineman and he is right in the lineman's path, so it has to be a head-on collision. How fast must the wide receiver be running if he wants to drop the lineman in his tracks and save the day?

A) 88 mph
B) 0.60 m/s
C) 8.3 m/s
D) 10 m/s

Question 48

A rocket obeys the principles of recoil. However, it is much more difficult to apply Newton's second law to a rocket because

A) Newton's three laws do not apply in outer space.
B) there is actually sideways momentum, because a rocket motor is just a well-controlled explosion.
C) the rocket pushes against air but the air is a fluid.
D) as the rocket motor fires the total mass of the rocket changes.

Question 49

A 60 kg boy standing on a skateboard with frictionless wheels and negligible mass throws a 3 kg ball straight up with a speed of 4 m/s. If the boy was at rest before the throw, his speed after the throw will be _________________.

Question 50

If the same impulse is applied to a ping-pong ball and a baseball, the change in the ping-pong ball's momentum will be _____________ the baseball's.

Question 51

An oil tanker heading due west, straight into a strong wind, reaches a speed of 5 m/s and then shuts down its engines to drift. The forward-facing flat surfaces of the tanker catch a total of 60,000 N of force from the wind. This wind force is pointing backwards, to the east. The tanker's mass is 100,000 metric tons, which is 100 million kg. If the wind blows at the same strength for 5 minutes, then how much has the wind changed the tanker's speed?

A) 1.2 m/s
B) 1.08 m/s
C) 0.018 m/s
D) 0.18 m/s

Question 52

Two astronauts of equal mass are holding on to each other and moving at a speed of 30 m/s. They push off of each other and one of the astronauts moves in the same direction as the two were initially moving but at 60 m/s. The velocity of the second astronaut is

A) 60 m/s backward.
B) 30 m/s backward.
C) zero.
D) 30 m/s forward.
E) 60 m/s forward.

Question 53

If a bullet is fired into a wooden block and remains lodged in the block, the collision was _________________.

Question 54

The total momentum of a system will change during a collision unless the ____________ force is zero.

Question 55

If heat, sound, or deformation of solid bodies results from a collision, there will be a change in the total ____________ __________.

Question 56

If you were standing on a cart that was at rest and free to roll (ignore friction) and someone threw a 10 kg ball at you, you would

A) not move if you caught the ball because you are more massive than the ball.
B) roll backward faster if you caught the ball.
C) roll backward faster if the ball bounced off of you elastically.
D) roll backward faster if you caught the ball higher above the ground.

Question 57

When a single boxcar in the freight yard hooks onto a stationary string of four boxcars, as in example 7.4, there is some kinetic energy lost. Which of the following could account for the missing energy?

A) Sound energy in the loud CLANG when they hook together.
B) Heat energy in the clamping mechanism between cars as it opens and then captures the fifth boxcar.
C) Both A and B

Question 58

If a bullet is fired into a solid wooden block and comes out the other side, the collision was _________________ inelastic.

Question 59

Consider a system containing three objects that move with different velocities. The objects can interact with each other through forces. In this system

A) the total kinetic energy of the objects will not change unless an outside force is applied.
B) the objects can only collide if an outside force is applied.
C) any collisions between the objects must be elastic.
D) the total momentum of the objects cannot change unless an outside force acts on the system.