Unit Test — Unit test Answers

For a movie stunt, an empty truck with a mass of 2000 kg goes 10 m/s and runs into a stopped car of mass 1000 kg. The truck then keeps moving and pushes the car along with it.

A

The collision is perfectly elastic.

B

Kinetic energy stays the same.

C

The momentum after the collision is greater than the momentum before the collision.

D

The speed of the combined vehicles is less than the initial speed of the truck.

2

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Two carts, one of mass 2m and one of mass m, approach each other with the same speed, v. When the carts collide, they hook together. Assume that positive momentum is to the right.Which graph best represents the momentum of both carts over time, before and after the collision?

A

A graph with momentum on the y axis measured in kilogram meters per second and time on the x axis measured in seconds. There are no values on the axes. There are two curves on the graph. The first starts above the x axis and is horizontal before curving downward to the x axis labeled 2 m cart. The second curve starts below the axis, the same distance below as the first one was above, and is horizontal before curving upward toward the x axis at the same time and labeled m cart. Where they meet is labeled Collision. Both curves meet at the x axis at the same time and are both on the x axis for a time period labeled Combined carts.

B

A graph with momentum on the y axis measured in kilogram meters per second and time on the x axis measured in seconds. There are no values on the axes. There are two curves on the graph. The first starts above the x axis and is horizontal before curving downward to the x axis labeled 2 m cart. The second curve starts below the axis, the same distance below as the first one was above, and is horizontal before curving upward toward the x axis at the same time and labeled m cart. Where they meet is labeled Collision. Both curves meet at the x axis at the same time and are both on the x axis for a time period labeled Combined carts.

C

A graph with momentum on the y axis measured in kilogram meters per second and time on the x axis measured in seconds. There are no values on the axes. There are two curves on the graph the first starts above the x axis and is horizontal before curving downward toward the x axis labeled 2 m cart. The second curve starts below the axis, a smaller distance below as the first one was above, and is horizontal before curving upward toward and crosses the x axis and is labeled m cart. Where they meet is labeled Collision. Both curves meet above the axis at the same time and both go horizontal above the x axis for a time period labeled Combined carts.

D

A graph with momentum on the y axis measured in kilogram meters per second and time on the x axis measured in seconds. There are no values on the axes. There are two curves on the graph the first starts above the x axis and is horizontal before curving downward toward the x axis labeled 2 m cart. The second curve starts below the axis, a smaller distance below as the first one was above, and is horizontal before curving upward toward and crosses the x axis and is labeled m cart. Where they meet is labeled Collision. Both curves meet above the axis at the same time and both go horizontal above the x axis for a time period labeled Combined carts.

3

Two blocks are initially at rest with a compressed spring between them. When the spring is released, the 2m block moves to the left and the m block moves to the right. This represents an inelastic collision in a closed system.

A

The total energy is zero.

B

The total momentum is zero.

C

The momentum of the m block is zero.

D

The momentum of the 2m block is zero.

4

Students perform an experiment in which they drop two eggs with equal mass from a balcony. In the first trial, the egg hits the ground and breaks. In the second trial, the egg hits a foam cushion and does not break or bounce.

A

The impulse was greater in the first experiment because the egg broke.

B

The impulse was greater in the second experiment because the egg did not break.

C

The impulse was the same in both experiments because the egg came to a stop.

D

The impulse cannot be determined without the mass and velocity of the eggs.

5

A baseball has a mass of 0.45 kg and is thrown with a speed of 25 m/s. What is the momentum of the baseball?

A

0.018 kg •

B

11 kg •

C

56 kg •

D

140 kg •

6

A 57 g tennis ball is traveling at 45 m/s to the right, when it hits a racket. The ball reverses direction and travels at 33 m/s. The ball is in contact with the racket for 0.0085 s.

A

1.8 N

B

12 N

C

81 N

D

520 N

7

Which formulas show the relationships between momentum, mass, and velocity? Check all that apply.p = mvp = p = m = p = v = v =

A

p = mv

B

p =

C

p =

D

m =

E

p =

F

v =

G

v =

8

Different forces were applied to five balls, and each force was applied for the same amount of time. The data is in the table.

A

It divides in half.

B

It does not change.

C

It doubles.

D

It quadruples.

9

Which cars have the same magnitude of momentum? Check all that apply.

A

car 1

B

car 2

C

car 3

D

car 4

E

car 5

10

An object with a mass of 1.5 kg changes its velocity from +15 m/s to +22 m/s during a time interval of 3.5 seconds. What impulse was delivered to the object?

A

3.0 N • s

B

11 N • s

C

25 N • s

D

56 N • s

11

Students are completing a lab in which they let a lab cart roll down a ramp. The students record the mass of the cart, the height of the ramp, and the velocity at the bottom of the ramp. The students then calculate the momentum of the cart at the bottom of the ramp.Which trial’s cart has the greatest momentum at the bottom of the ramp?

A

trial 1, because this trial has the greatest velocity

B

trial 2, because this trial has the greatest ramp height

C

trial 3, because this trial has a large mass and a large velocity

D

trial 4, because this trial has the greatest mass

12

Question text not available

Answer not available

13

What are possible formulas for impulse? Check all that apply.J = FtJ = J = FvJ = J = mvJ = p

A

J = Ft

B

J =

C

J = Fv

D

J =

E

J = mv

F

J = p

14

A 50 kg boy runs and jumps with a forward velocity of 1.5 m/s into a 125 kg stationary boat.

A

0.43 m/s, forward

B

0.43 m/s, backward

C

1.1 m/s, forward

D

1.1 m/s, backward

15

2.24.48.813

A

2.2

B

4.4

C

8.8

D

13

16

Two identical carts travel at the same speed toward each other, and then a collision occurs. The graphs show the momentum of each cart as a function of time, both before and after the collision.Which graph shows a perfectly inelastic collision?

A

There is a graph with time in seconds on the x axis and the y axis is labeled P in kilogram meters per second. There is a red horizontal line that drops down below the x axis and is the farther away from the x axis and a horizontal line. A blue line is the mirror image starting below the x axis and ending above the x axis. The red line is labeled car A and a blue line labeled car B. At the point both graphs cross the x axis is labeled collision.

B

A graph with momentum on the y axis measured in kilogram meters per second and time on the x axis measured in seconds. There are no values on the axes. There are two curves on the graph. The first starts above the x axis and is horizontal before curving downward to the x axis labeled 2 m cart. The second curve starts below the axis, the same distance below as the first one was above, and is horizontal before curving upward toward the x axis at the same time and labeled m cart. Where they meet is labeled Collision. Both curves meet at the x axis at the same time and are both on the x axis for a time period labeled Combined carts.

C

A graph with momentum on the y axis measured in kilogram meters per second and time on the x axis measured in seconds. There are no values on the axes. There are two curves on the graph the first starts above the x axis and is horizontal before curving downward toward the x axis labeled 2 m cart. The second curve starts below the axis, a smaller distance below as the first one was above, and is horizontal before curving upward toward and crosses the x axis and is labeled m cart. Where they meet is labeled Collision. Both curves meet above the axis at the same time and both go horizontal above the x axis for a time period labeled Combined carts.

D

There is a graph with time in seconds on the x axis and the y axis is labeled P in kilogram meters per second. There is a red horizontal line that drops down below the x axis and is then farther away from the x axis and a horizontal line. A blue line is the mirror image starting below the x axis and ending above the x axis. The red line is labeled car A and a blue line labeled car B. At the point both graphs cross the x axis is labeled collision.

17

A boy and his skateboard have a combined mass of 65 kg. What is the speed of the boy and skateboard if they have a momentum of 275 kg • ?

A

0 m/s

B

0.24 m/s

C

4.2 m/s

D

8.5 m/s

18

What best describes an impulse acting on an object?

A

the net force on an object divided by the time of impact

B

the velocity of an object divided by its mass

C

the product of an object's mass and the time of force impact

D

the product of an object's mass and its change in velocity

19

What type of relationship exists between momentum and mass?

A

direct

B

inverse

C

logarithmic

D

quadratic

20

A 0.060 kg ball hits the ground with a speed of –32 m/s. The ball is in contact with the ground for 45 milliseconds and the ground exerts a +55 N force on the ball.

A

9.3 m/s

B

12 m/s

C

41 m/s

D

73 m/s

Unit Test — Unit test Answers

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