Q: A 2-kg object moves with a velocity of 10 m/s at 37° above the horizontal. What is the magnitude of its momentum?

$$p = 2 \times 10 = 20\ \mathrm{kg \cdot m/s}$$

Q: A 150-g rubber ball moving at 40 m/s to the right hits a wall and bounces back at 45 m/s to the left. What is the impulse delivered to the ball?

$$J = 0.15 \times (-45) - 0.15 \times 40 = -6.75 - 6 = -12.75\ \mathrm{kg \cdot m/s}$$

Q: Two objects, A (4 kg) moving at 12 m/s to the right and B (5 kg) moving at 9 m/s to the left, collide. What is the total momentum of the system before the collision?

$$p_{sys} = 4 \times 12 + 5 \times (-9) = 48 - 45 = 3\ \mathrm{kg \cdot m/s}$$

Q: A 4-kg sniper rifle fires a 5-g bullet at 600 m/s. What is the recoil speed of the rifle?

$$v_{rifle} = -\frac{0.005 \times 600}{4} = -0.75\ \mathrm{m/s}$$

Q: A 10-g bullet is fired into a 5-kg block of wood and becomes embedded. If the final speed of the system is 0.6 m/s, what was the original speed of the bullet?

$$v_{bullet} = \frac{(5 + 0.01) \times 0.6}{0.01} = 300.6\ \mathrm{m/s}$$

Question 1

Which of the following best describes momentum?

Accepted Answer

A vector quantity that measures how difficult it is to stop a moving object.

Question 2

A 2-kg object moves with a velocity of 10 m/s at 37° above the horizontal. What is the magnitude of its momentum?

Accepted Answer

$$p = 2 	imes 10 = 20\ \mathrm{kg \cdot m/s}$$

Question 3

Which equation correctly relates impulse to the change in momentum?

Accepted Answer

$$J = F \Delta t = m v_f - m v_0$

Question 4

A 100-g ball is thrown with a velocity of 30 m/s and is in contact with your hand for 0.2 s. What is the average force exerted on the ball?

Accepted Answer

$$F_{avg} = 15\ \mathrm{N}$$

Question 5

A 150-g rubber ball moving at 40 m/s to the right hits a wall and bounces back at 45 m/s to the left. What is the impulse delivered to the ball?

Accepted Answer

$$J = 0.15 	imes (-45) - 0.15 	imes 40 = -6.75 - 6 = -12.75\ \mathrm{kg \cdot m/s}$$

Question 6

A 1200-kg car moving at 20 m/s crashes into a wall and comes to rest after compressing 1.0 m into the wall. Assuming constant acceleration, what is the average force exerted by the wall?

Accepted Answer

$$F = \frac{m v^2$}{2 \Delta x}$$

Question 7

The area under a force vs. time ($$F vs$$. $$t) $$graph represents:

Accepted Answer

The impulse delivered to the object

Question 8

Two objects, A (4 kg) moving at 12 m/s to the right and B (5 kg) moving at 9 m/s to the left, collide. What is the total momentum of the system before the collision?

Accepted Answer

$$p_{sys} = 4 	imes 12 + 5 	imes (-9) = 48 - 45 = 3\ \mathrm{kg \cdot m/s}$$

Question 9

A 4-kg sniper rifle fires a 5-g bullet at 600 m/s. What is the recoil speed of the rifle?

Accepted Answer

$$v_{rifle} = -\frac{0.005 	imes 600}{4} = -0.75\ \mathrm{m/s}$$

Question 10

Which of the following is true for a perfectly inelastic collision?

Accepted Answer

Momentum is conserved, but mechanical energy is not.

Question 11

A 10-g bullet is fired into a 5-kg block of wood and becomes embedded. If the final speed of the system is 0.6 m/s, what was the original speed of the bullet?

Accepted Answer

$$v_{bullet} = \frac{(5 + 0.01) 	imes 0.6}{0.01} = 300.6\ \mathrm{m/s}$$

Question 12

Which of the following is a characteristic of an elastic collision?

Accepted Answer

Both momentum and mechanical energy are conserved.

Question 13

A 70-kg hockey player skates at 5 m/s and collides head-on with a 110-kg player at 4 m/s. If they stick together, what is their final velocity?

Accepted Answer

$$v_f = \frac{70 	imes 5 + 110 	imes (-4)}{70 + 110} = -1.5\ \mathrm{m/s}$$

Question 14

In a head-on elastic collision between two objects of equal mass, what happens to their velocities?

Accepted Answer

They exchange velocities.

Question 15

Which equation gives the center of mass $$X_{com}$$ for two masses $$m_1$$ and $$m_2 at $$positions $$x_1$$ and $$x_2$$?

Accepted Answer

$$X_{com} = \frac{m_1$ x_1$ + m_2$ x_2$}{m_1$ + m_2$}$$

Question 16

A 40-kg skater and a 3-kg skateboard both move at 10 m/s. The skater jumps on the board. What is the final speed of the system?

Accepted Answer

$$v_f = \frac{40 	imes 10 + 3 	imes 10}{40 + 3} = 10\ \mathrm{m/s}$$

Question 17

Which of the following is NOT a step in solving a conservation of momentum problem involving a collision?

Accepted Answer

Calculate the work done by friction during the collision.

Question 18

A 20-kg crate moving at 40 m/s collides and sticks to a 30-kg crate at rest. After the collision, the crates move up a frictionless incline. How high do the crates travel before stopping?

Accepted Answer

$$h = \frac{\frac{1}{2} (20 + 30) v^2$}{(20 + 30) g}$$

Momentum & Impulse: Structured Study Notes for College Physics

Study Guide - Practice Questions

Study Guide - Flashcards