Physics 1 - Chapter 7 - Linear Momentum Conceptual Questions

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?

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.

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?

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.

A 4kg 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.

a) 3 m/s

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.

a) long.

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.

a) speed.

A ball is moving at 4 m/s and has a momentum of 48 kg*m/s. What is the balls mass? a) 4 kg b) 12 kg c) 48 kg d) 192 kg e) none of the above

b) 12 kg

The impulse-momentum relationship is a direct result of a) Newton's first law b) Newton's second law c) Newton's third law

b) Newton's second law.

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.

b) doubled.

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.

b) the change in momentum

The distinction between impulse and force involves the a) distance the fore acts. b) time the force acts. c) difference between acceleration and velocity. d) mass and its effect on resisting a change in momentum.

b) time the force acts.

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.

c) about 10 times.

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.

c) both

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.

c) momentum

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.

c) momentum.

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.

c) time of catch is increased.

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

d) all of the above

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

d) all of the above.

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

A) 0 kg∙m/s

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

A) 0.5 m/s.

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.

A) 1/2 m/s.

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.

A) decreases.

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.

A) distance that a force acts.

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.

A) greater.

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

A) jumper.

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

A) on the wall.

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.

A) twice as much work.

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.

A) zero.

An unfortunate bug spatters on the windshield of a moving car. Describe the forces, impulses, momentum changes, and accelerations of both the bug and the car.

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 and 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 unnoticed.

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.

B) 1 kg∙m/s.

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.

B) 2000 N

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

B) The astronaut will never catch the first bounce.

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

B) a pickup truck speeding along a highway

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.

B) decreases.

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.

B) decreases.

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.

B) full length.

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

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

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

B) impulse.

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

B) longer time to stop

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

B) recoiling gun.

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?

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.

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.

C) 0.83 m/s.

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

C) 1 unit.

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.

C) 1/3 m/s.

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

C) 1/6 m/s.

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.

C) 1/6 m/s.

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

C) 1/6 m/s.

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.

C) 5/6 m/s.

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

C) 6 m/s

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.

C) 8.0 N.

The conservation of momentum is closely related to A) Newton's first law. B) Newton's second law. C) Newton's third law.

C) Newton's third law.

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

C) both the same

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

C) both the same

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

C) both the same

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.

C) masses.

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

C) the same

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.

D) 0.05 m/s.

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

D) 1 m/s.

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

D) all of the above

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

D) exhaust gases.

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

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

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

D) none of the above

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

E) none of the above

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

E) not enough information