PHY 101: Ch. 6 Homework and Quiz

A 3.00-kg blob of putty moving at 3.00 m/s slams into a 5.00-g blob of putty at rest. Calculate the speed of the two stuck-together blobs of putty immediately after colliding.

3.00 m/s

A cannonball shot from a cannon with a long barrel will emerge with greater speed because the cannonball receives a greater a. average force b. impulse c. both of the above d. none of the above

b. impulse

A 2.8-kg blob of putty moving at 4.0 m/s slams into a 2.8-kg blob of putty at rest. Calculate the speed of the two stuck-together blobs of putty immediately after colliding.

2.0 m/s

The change in momentum that occurs when a 1.0 kg ball traveling at 4.0 m/s strikes a wall and bounces back at 2.0 m/s is a. 6 kg m/s. b. 4 kg m/s. c. 2 kg m/s. d. 8 kg m/s.

a. 6 kg m/s.

When a dish falls, will the change in momentum be less if it lands on a carpet than if it lands on a hard floor? (Careful!) a. No, both are the same. b. Yes, less if it lands on the carpet. c. No, less if it lands on a hard floor. d. No, more if it lands on a hard floor

a. no, both are the same

A 5000-kg freight car moving at 2 m/s runs into a 10,000-kg freight car at rest. They couple upon collision and move away as one body at a. 1/3 m/s. b. 2/3 m/s. c. 1 m/s. d. 2 m/s.

b. 2/3 m/s.

A 4 kg ball has a momentum of 12 kg m/s. What is the ball's speed? a. 4 m/s b. 3 m/s c. 48 m/s d. 12 m/s none of these

b. 3 m/s

Two 5000-kg rail cars roll without friction (one at 1 m/s, the other at 2 m/s) toward each other on a level track. They collide, couple, and roll together with a combined momentum of a. 10,000 kg m/s. b. 5000 kg m/s. zero. c. 15,000 kg m/s.

b. 5000 kg m/s. zero.

When the force that produces an impulse acts for twice as much time, the impulse is a. not changed b. doubled c. quadrupled d. halved

b. doubled

Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A? a. The speed of car B is zero. b. The speed of car B is twice the initial speed of car A. c. The speed of car B is equal to the initial speed of A. d. The speed of car B is half the initial speed of car A.

c. The speed of car B is equal to the initial speed of A.

You're driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum during the time of contact? a. your car b. the bug c. both the same

c. both the same

A moving object has a. momentum b. energy c. speed d. all of the above

d. all of the above

According to the impulse-momentum equation Ft = change in (mv), a person will suffer less injury falling on a wooden floor which "gives" than on a more rigid cement floor. The "F" in the above equation stands for the force exerted on the a. only the person. b. only the floor. c. either the force on the person or the force on the floor d. the sum of the force on the person and the force on the floor

c. either the force on the person or the force on the floor

Padded dashboards in cars are safer in an accident than nonpadded ones because an occupant hitting the dash has a. increased momentum. b. decreased impulse. c. increased time of impact. d. decreased time of impact.

c. increased time of impact

Padded dashboards in cars are safer in an accident than nonpadded ones because an occupant hitting the dash has a. decreased impulse. b. increased momentum. c. increased time of impact. d. decreased time of impact.

c. increased time of impact

A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels as fast on the Moon, is its momentum a. more b. less c. same

c. same

What is the magnitude of the impulse on an 8.2-kg ball rolling at 3.0 m/s when it bumps into a pillow and stops?

25 N*s

A 5.4-kg fish swimming 1.0 m/s swallows an absentminded 1.0-kg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch. Find speed of the approaching smaller fish before lunch.

5.4 m/s

Why is it advantageous to roll with the punch in boxing?

Rolling with the punch increases contact time, which decreases the force

A 1000-kg car moving at 10 m/s brakes to a stop in 5 s. The average braking force is a. 5000 N. b. 2000 N. c. 1000 N. d. 3000 N. e. 4000 N.

b. 2000 N.

Two vehicles with equal magnitudes of momentum traveling at right angles to each other undergo an inelastic collision. The combined wreck moves in a direction a. at 45 degrees to the direction of either car before collision. b. at some angle other than 45 degrees. c. parallel to either of the cars before collision.

a. at 45 degrees to the direction of either car

An astronaut , floating alone in outer space, throws a baseball. If the ball floats away at a speed of 20 meters per second, the astronaut will a. move in the opposite direction at a speed of 20 m/s. b. not move as stated in any of the above choices. c. move in the opposite direction, but at a lower speed. d. move in the opposite direction but at a higher speed.

c. move in the opposite direction, but at a lower speed.

Which of the following has the largest momentum relative to the Earth's surface? a. a dog running down the street b. the Science building on campus c. a Mack truck parked in a parking lot d. a tightrope walker crossing Niagara Falls e. a pickup truck speeding along a highway

e. a pickup truck speeding along a highway

What is the momentum of a 46-kg carton that slides at 3.8 m/s across an icy surface?

170 kg*m/s

What impulse occurs when an average force of 7.0 N is exerted on a cart for 2.7 s?

19 kg*m/s

How much impulse stops a 56-kg carton sliding at 3.4 m/s when it meets a rough surface?

190 N*s

Joanne drives her car with a mass of 1000 kg at a speed of 23 m/s. Find a road friction force that is need to bring her car to a halt in 15 s.

1500 N

What impulse occurs when the force of 15 N acts on the cart for the time 6.0 s?

90 kg*m/s

A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force experienced by her hand is a. identical to the force applied to the block. b. less than the force applied to the cement block. c. more than the force applied to the block. d. zero. e. impossible to predict without additional information.

a. identical to the force applied to the block.

When the speed of an object is doubled, its momentum a. remains unchanged in accord with the conservation of momentum. b. doubles. c. quadruples. d. decreases.

b. doubles

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 to the force that stops the car, the force needed to stop the truck is a. the same. b. greater. c. smaller.

b. greater

Freight car A is moving toward identical freight car B that is at rest. When they collide, both freight cars couple together. Compared with the initial speed of freight car A, the speed of the coupled freight cars is a. the same. b. half. c. twice. d. None of the above.

b. half

Cassy can get more force on the bricks she breaks with a blow of her bare hand when _______. a. she toughens her hand beforehand b. her hand is made to bounce from the bricks c. she exerts follow through d. she does so with great determination

b. her hand is made to bounce from the bricks

When you are in the way of a fast-moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a a. short time b. long time c. same way either way

b. long time

A fast-moving car hitting a haystack or hitting a cement wall produces vastly different results. 1. Do both experience the same change in momentum? 2. Do both experience the same impulse? 3. Do both experience the same force? a. Yes for all three b. Yes for 1 and 2 c. No for all three d. No for 1 and 2

b.yes for 1 and 2

Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet? a. twice the sum of their original momentums b. half the sum of their original momentums c. 0 d. impossible to determine without additional information

c. 0

A ball is moving at 3 m/s and has a momentum of 48 kg m/s. What is the ball's mass? a. 12 kg b. 4 kg c. 16 kg d. 144 kg d. none of these

c. 16 kg

A 5000-kg freight car runs 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 car? a. 4 m/s b. 5 m/s c. 6 m/s d. 8 m/s

c. 6 m/s 10,000+5,000= 15,000 (momentum Car A + Car B) 15,000/5,000 = 3 * 2 = 6

If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A? a. Their speed is zero. b. Their speed is equal to the initial speed of car A. c. Their speed is half the initial speed of car A. d. Their speed is twice the initial speed of car A.

c. Their speed is half the initial speed of car A.

It is correct to say that impulse is equal to a. velocity multiplied by time. b. momentum. c. the change in momentum it produces. d. the force multiplied by the distance the force acts.

c. the change in momentum it produces

Part A Part complete When a falling firecracker explodes, the momenta of its pieces _______. a. disintegrate b. are conserved only if the fragments eject in one direction c. vectorially add to equal the initial momentum of the firecracker d. illustrate a case in which momentum is not conserved

c. vectorially add to equal the initial momentum of the firecracker

A car traveling along the highway needs a certain amount of force exerted on it to stop it in a certain distance. More stopping force is required when the car has a. more momentum. b. more mass. c. less stopping distance. d. all of these e. none of these

d. all of these

To catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because the a. time of impact is decreased b. force of impact is reduced c. relative velocity is less d. time of impact is increased

d. time of impact is increased