Question 1

In a collision between two unequal masses, which mass receives a greater magnitude impulse?

Accepted Answer

A)  the larger mass 
B)  the smaller mass 
C)  They receive equal impulses. 
A)  the larger mass 
B)  the smaller mass 
C)  They receive equal impulses. C

Question 2

Two astronauts, of masses 60 kg and 80 kg, are initially right next to each other and at rest in outer space. They suddenly push each other apart. What is their separation after the heavier astronaut has moved 12 m?

Accepted Answer

A)  9.0 m 
B)  16 m 
C)  21 m 
D)  24 m 
E)  28 m 
A)  9.0 m 
B)  16 m 
C)  21 m 
D)  24 m 
E)  28 m E

Question 3

A forklift pushes a 100-kg crate, starting from rest, with a horizontal force of magnitude F. The graph in the figure shows the x component of this force as a function of time. What is the instantaneous velocity of the crate at time t = 10 s?

Accepted Answer

A)  25 cm/s 
B)  0.00 cm/s 
C)  75 cm/s 
D)  -25 cm/s 
E)  -75 cm/s 
A)  25 cm/s 
B)  0.00 cm/s 
C)  75 cm/s 
D)  -25 cm/s 
E)  -75 cm/s E

Question 4

Two astronauts, of masses 60 kg and 80 kg, are initially right next to each other and at rest in outer space. They suddenly push each other apart. How far has the heavier astronaut moved when the lighter astronaut has moved 12 m?

Accepted Answer

A)  16 m 
B)  9.0 m 
C)  21 m 
D)  7.0 m 
E)  12 m 
A)  16 m 
B)  9.0 m 
C)  21 m 
D)  7.0 m 
E)  12 m

Question 5

A 0.140 kg baseball is thrown horizontally with a velocity of 28.9 m/s. It is struck with a constant horizontal force that lasts for 1.85 ms, which results in a velocity of 37.0 m/s in the opposite direction. What was the magnitude of the horizontal force?

Accepted Answer

A)  0.613 kN 
B)  2.19 kN 
C)  2.80 kN 
D)  4.99 kN 
A)  0.613 kN 
B)  2.19 kN 
C)  2.80 kN 
D)  4.99 kN

Question 6

A puck with a mass m1 = 50 g moving at 1.0 m/s approaches a stationary puck with a mass m2 = 100 g on a frictionless air table, and they undergo a sudden two-dimensional elastic collision. After the collision, both pucks have identical speeds, but travel in different directions. What is the angle between the original and final paths of puck with mass m1?

Accepted Answer

A)  30° 
B)  60° 
C)  90° 
D)  120° 
E)  150° 
A)  30° 
B)  60° 
C)  90° 
D)  120° 
E)  150°

Question 7

A rocket explodes into two fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is

Accepted Answer

A)  25 times as great as the momentum change of the heavier fragment. 
B)  The same as the momentum change of the heavier fragment. 
C)  1/25 as great as the momentum change of the heavier fragment. 
D)  5 times as great as the momentum change of the heavier fragment. 
E)  1/4 as great as the momentum change of the heavier fragment. 
A)  25 times as great as the momentum change of the heavier fragment. 
B)  The same as the momentum change of the heavier fragment. 
C)  1/25 as great as the momentum change of the heavier fragment. 
D)  5 times as great as the momentum change of the heavier fragment. 
E)  1/4 as great as the momentum change of the heavier fragment.

Question 8

A 14-cm diameter champagne bottle rests on its side on top of a frictionless horizontal table. Suddenly, the cork pops and the bottle slides backward, covering a distance of $22.0 \mathrm {~cm}$ in $0.44 \mathrm {~s}$ If the mass of the bottle is 500 times the mass of the cork, find the distance from the original position that the cork will land on the table. Neglect air resistance and assume that the cork is very small compared to the bottle.

Accepted Answer

A)  3000 cm 
B)  60 m 
C)  85 m 
D)  8.5 cm 
A)  3000 cm 
B)  60 m 
C)  85 m 
D)  8.5 cm

Question 9

A 2.0-kg ball moving eastward at 3.0 m/s suddenly collides with and sticks to a 4.0-kg ball moving northward at 2.0 m/s. What is the magnitude of the momentum of this system just after the collision?

Accepted Answer

A)  14 kg ∙ m/s 
B)  2.0 kg ∙ m/s 
C)  10 kg ∙ m/s 
D)  6.0 kg ∙ m/s 
E)  8.0 kg ∙ m/s 
A)  14 kg ∙ m/s 
B)  2.0 kg ∙ m/s 
C)  10 kg ∙ m/s 
D)  6.0 kg ∙ m/s 
E)  8.0 kg ∙ m/s

Question 10

A light-weight potter's wheel, having a moment of inertia of $24 \mathrm {~kg} \cdot \mathrm { m } ^ { 2 }$ is spinning freely at 40.0 rpm. The potter drops a small but dense lump of clay onto the wheel, where it sticks a distance 1.2 m from the rotational axis. If the subsequent angular speed of the wheel and clay is 32 rpm, what is the mass of the clay?

Accepted Answer

A)  4.2 kg 
B)  2.8 kg 
C)  3.7 kg 
D)  4.6 kg 
A)  4.2 kg 
B)  2.8 kg 
C)  3.7 kg 
D)  4.6 kg

Question 11

A figure skater rotating at 5.00 rad/s with arms extended has a moment of inertia of 2.25 kg ∙ m2. If he pulls in his arms so his moment of inertia decreases to 1.80 kg ∙ m2, what will be his new angular speed?

Accepted Answer

A)  2.25 rad/s 
B)  4.60 rad/s 
C)  6.25 rad/s 
D)  0.81 rad/s 
A)  2.25 rad/s 
B)  4.60 rad/s 
C)  6.25 rad/s 
D)  0.81 rad/s

Question 12

A 0.14-kg baseball is dropped from rest from a height of 2.0 m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance?

Accepted Answer

A)  0.28 kg ∙ m/s 
B)  0.88 kg ∙ m/s 
C)  0.44 kg ∙ m/s 
D)  0.62 kg ∙ m/s 
E)  1.4 kg ∙ m/s 
A)  0.28 kg ∙ m/s 
B)  0.88 kg ∙ m/s 
C)  0.44 kg ∙ m/s 
D)  0.62 kg ∙ m/s 
E)  1.4 kg ∙ m/s

Question 13

The graph in the figure shows the x component F of the net force that acts for 10 s on a 100-kg crate. What is the change in the momentum of the crate during the 10 s that this force acts?

Accepted Answer

A)  -100 kg ∙ m/s 
B)  -25 kg ∙ m/s 
C)  75 kg ∙ m/s 
D)  -75 kg ∙ m/s 
E)  25 kg ∙ m/s 
A)  -100 kg ∙ m/s 
B)  -25 kg ∙ m/s 
C)  75 kg ∙ m/s 
D)  -75 kg ∙ m/s 
E)  25 kg ∙ m/s

Question 14

A steady horizontal force lasting for 2.1 s gives a 1.25 kg object an acceleration of 3.2 m/s2 on a frictionless table. What impulse does this force give to the object?

Accepted Answer

A)  26 kg ∙ m/s 
B)  11 kg ∙ m/s 
C)  8.4 kg ∙ m/s 
D)  2.6 kg ∙ m/s 
A)  26 kg ∙ m/s 
B)  11 kg ∙ m/s 
C)  8.4 kg ∙ m/s 
D)  2.6 kg ∙ m/s

Question 15

A 900-kg car traveling east at 15.0 m/s suddenly collides with a 750-kg car traveling north at 20.0 m/s. The cars stick together after the collision. What is the speed of the wreckage just after the collision?

Accepted Answer

A)  6.10 m/s 
B)  12.2 m/s 
C)  25.0 m/s 
D)  35.0 m/s 
E)  17.3 m/s 
A)  6.10 m/s 
B)  12.2 m/s 
C)  25.0 m/s 
D)  35.0 m/s 
E)  17.3 m/s

Question 16

In a police ballistics test, a 10.0-g bullet moving at 300 m/s is fired into a 1.00-kg block at rest. The bullet goes through the block almost instantaneously and emerges with 50.0% of its original speed. What is the speed of the block just after the bullet emerges?

Accepted Answer

A)  1.50 m/s 
B)  2.97 m/s 
C)  3.00 m/s 
D)  273 m/s 
A)  1.50 m/s 
B)  2.97 m/s 
C)  3.00 m/s 
D)  273 m/s

Question 17

A 100-g ball falls from a window that is 12 m above ground level and experiences no significant air resistance as it falls. What is its momentum when it strikes the ground?

Accepted Answer

A)  3.3 kg ∙ m/s 
B)  4.8 kg ∙ m/s 
C)  1.8 kg ∙ m/s 
D)  1.5 kg ∙ m/s 
E)  2.4 kg ∙ m/s 
A)  3.3 kg ∙ m/s 
B)  4.8 kg ∙ m/s 
C)  1.8 kg ∙ m/s 
D)  1.5 kg ∙ m/s 
E)  2.4 kg ∙ m/s

Question 18

A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct? (There could be more than one correct choice.)

Accepted Answer

A)  The ball had the same momentum just before and just after the bounce. 
B)  The magnitude of the ball's momentum was the same just before and just after the bounce. 
C)  The ball's momentum was conserved during the bounce. 
D)  None of the above statements are correct. 
A)  The ball had the same momentum just before and just after the bounce. 
B)  The magnitude of the ball's momentum was the same just before and just after the bounce. 
C)  The ball's momentum was conserved during the bounce. 
D)  None of the above statements are correct.

Question 19

A 24.5-kg child is standing on the outer edge of a horizontal merry-go-round that has a moment of inertia of $989 \mathrm {~kg} \cdot \mathrm { m } ^ { 2 }$ about a vertical axis through its center and a radius of 2.40 m. The entire system (including the child) is initially rotating at 0.180 rev/s. Find the angular velocity if the child moves to a new position 1.10 m from the center of the merry-go-round.

Accepted Answer

The answer of A 24.5-kg child is standing on the...

Question 20

Which of the following quantities are units of impulse? (There could be more than one correct choice.)

Accepted Answer

A)  N ∙ m 
B)  kg ∙ s/m 
C)  kg ∙ m/s 
D)  N ∙ s 
E)  kg ∙ m2/s2 
A)  N ∙ m 
B)  kg ∙ s/m 
C)  kg ∙ m/s 
D)  N ∙ s 
E)  kg ∙ m2/s2

Exam 9: Momentum

In a collision between two unequal masses, which mass receives a greater magnitude impulse?

Two astronauts, of masses 60 kg and 80 kg, are initially right next to each other and at rest in outer space. They suddenly push each other apart. What is their separation after the heavier astronaut has moved 12 m?

A forklift pushes a 100-kg crate, starting from rest, with a horizontal force of magnitude F. The graph in the figure shows the x component of this force as a function of time. What is the instantaneous velocity of the crate at time t = 10 s?

Two astronauts, of masses 60 kg and 80 kg, are initially right next to each other and at rest in outer space. They suddenly push each other apart. How far has the heavier astronaut moved when the lighter astronaut has moved 12 m?

A 0.140 kg baseball is thrown horizontally with a velocity of 28.9 m/s. It is struck with a constant horizontal force that lasts for 1.85 ms, which results in a velocity of 37.0 m/s in the opposite direction. What was the magnitude of the horizontal force?

A rocket explodes into two fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is

A 2.0-kg ball moving eastward at 3.0 m/s suddenly collides with and sticks to a 4.0-kg ball moving northward at 2.0 m/s. What is the magnitude of the momentum of this system just after the collision?

A figure skater rotating at 5.00 rad/s with arms extended has a moment of inertia of 2.25 kg ∙ m2. If he pulls in his arms so his moment of inertia decreases to 1.80 kg ∙ m2, what will be his new angular speed?

A 0.14-kg baseball is dropped from rest from a height of 2.0 m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance?

The graph in the figure shows the x component F of the net force that acts for 10 s on a 100-kg crate. What is the change in the momentum of the crate during the 10 s that this force acts?

A steady horizontal force lasting for 2.1 s gives a 1.25 kg object an acceleration of 3.2 m/s2 on a frictionless table. What impulse does this force give to the object?

A 900-kg car traveling east at 15.0 m/s suddenly collides with a 750-kg car traveling north at 20.0 m/s. The cars stick together after the collision. What is the speed of the wreckage just after the collision?

In a police ballistics test, a 10.0-g bullet moving at 300 m/s is fired into a 1.00-kg block at rest. The bullet goes through the block almost instantaneously and emerges with 50.0% of its original speed. What is the speed of the block just after the bullet emerges?

A 100-g ball falls from a window that is 12 m above ground level and experiences no significant air resistance as it falls. What is its momentum when it strikes the ground?

A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct? (There could be more than one correct choice.)

Which of the following quantities are units of impulse? (There could be more than one correct choice.)

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A figure skater rotating at 5.00 rad/s with arms extended has a moment of inertia of 2.25 kg ∙ m². If he pulls in his arms so his moment of inertia decreases to 1.80 kg ∙ m², what will be his new angular speed?

A steady horizontal force lasting for 2.1 s gives a 1.25 kg object an acceleration of 3.2 m/s² on a frictionless table. What impulse does this force give to the object?