Q: A train of mass $$m = 2 \times 10^5$\ \mathrm{kg} is $$moving at $$v = 40\ \mathrm{m/s}. $$What is its linear momentum?

$$p = 8 \times 10^6$\ \mathrm{kg\cdot m/s}$$

Question 1

A group of students is pushing a large snowball across a field, as shown in the image. If the total mass of the snowball is $$m = 80\ \mathrm{kg}$$ and they accelerate it from rest to $$v = 2\ \mathrm{m/s} in$$ $$t = 10\ \mathrm{s}$$, what is the magnitude of the average net force they exert on the snowball?

Accepted Answer

$$F = 16\ \mathrm{N}$$

Question 2

Which of the following best describes the physical meaning of linear momentum $$\vec{p}$$ for a moving object?

Accepted Answer

It is the product of the object's mass and its velocity: $$\vec{p} = m\vec{v}$$

Question 3

A hammer of mass $$M is $$dropped from a height $$h$$ onto a nail, driving it into a piece of wood. If the hammer is instead dropped from a greater height $$2h$$, what happens to the momentum of the hammer just before impact?

Accepted Answer

The momentum increases by a factor of $$\sqrt{2}$$

Question 4

A train of mass $$m = 2 	imes 10^5$\ \mathrm{kg} is $$moving at $$v = 40\ \mathrm{m/s}. $$What is its linear momentum?

Accepted Answer

$$p = 8 	imes 10^6$\ \mathrm{kg\cdot m/s}$$

Question 5

Two ice skaters, Skater A ($$m_1 = 60$$\ \mathrm{kg}$$) and Skater B (m_2$ = 40\ \mathrm{kg}$$), push off from each other and move in opposite directions. If Skater A moves at $$v_1 = 3$$\ \mathrm{m/s}$$, what is the velocity of Skater B, assuming they started from rest?

Accepted Answer

$$v_2 = -4.5$$\ \mathrm{m/s}$$

Question 6

A car of mass $$m_1 = 1000$$\ \mathrm{kg}$$ moving at v_1$ = 20\ \mathrm{m/s}$$ collides with a stationary car of mass $$m_2 = 1500$$\ \mathrm{kg}$$. If the two cars stick together after the collision, what is their common velocity immediately after the collision?

Accepted Answer

$$v = 8\ \mathrm{m/s}$$

Question 7

Which of the following statements about the conservation of momentum is correct?

Accepted Answer

The total momentum of a system remains constant if no external force acts on it.

Question 8

A ball of mass $$m = 0.5\ \mathrm{kg} is $$thrown horizontally at $$v = 10\ \mathrm{m/s}$$ and hits a wall, bouncing back with the same speed in the opposite direction. What is the change in the ball's momentum?

Accepted Answer

$$\Delta p = -10\ \mathrm{kg\cdot m/s}$$

Question 9

A force $$F$$ acts on a body of mass $$m$$ for a time interval $$\Delta t$$, changing its velocity from $$v_0 to$$ $$v. $$Which equation correctly relates the impulse to the change in momentum?

Accepted Answer

$$F \Delta t = m v - m v_0$

Question 10

A skateboarder of mass $$m_1 = 50$$\ \mathrm{kg}$$ throws a ball of mass m_2$ = 2\ \mathrm{kg}$$ forward at $$v_2 = 5$$\ \mathrm{m/s}$$ while standing still on a frictionless surface. What is the velocity of the skateboarder after throwing the ball?

Accepted Answer

$$v_1 = -0.2$$\ \mathrm{m/s}$$

Question 11

A bullet of mass $$m = 0.01\ \mathrm{kg} is $$fired at $$v = 400\ \mathrm{m/s}$$ into a stationary block of mass $$M = 2\ \mathrm{kg} on a $$frictionless surface. If the bullet embeds in the block, what is their velocity after the collision?

Accepted Answer

$$v = 1.98\ \mathrm{m/s}$$

Question 12

Which of the following best explains why a heavier hammer drives a nail deeper into wood than a lighter hammer, assuming both are swung at the same speed?

Accepted Answer

The heavier hammer has greater momentum, so it delivers a larger impulse to the nail.

Question 13

A moving car of mass $$m$$ collides with a stationary truck of mass $$2m. If $$the collision is perfectly inelastic, what fraction of the car's initial momentum does the combined mass have after the collision?

Accepted Answer

$$\dfrac{1}{3}$$

Question 14

A soccer player kicks a stationary ball of mass $$0.4\ \mathrm{kg}$$, giving it a velocity of $$15\ \mathrm{m/s}. If $$the player's foot was in contact with the ball for $$0.02\ \mathrm{s}$$, what was the average force exerted on the ball?

Accepted Answer

$$F = 300\ \mathrm{N}$$

Question 15

Which of the following is NOT a correct statement about momentum?

Accepted Answer

Momentum is a scalar quantity.

Question 16

A 70 kg person jumps off a stationary boat of mass 130 kg and moves forward at 3 m/s. What is the velocity of the boat immediately after the jump?

Accepted Answer

$$v = -1.62\ \mathrm{m/s}$$

Question 17

A force-time graph for a collision shows a sharp peak over a short time interval. What does the area under the curve represent?

Accepted Answer

The impulse delivered to the object

Question 18

A 0.2 kg tennis ball moving at 10 m/s strikes a wall and rebounds in the opposite direction at 8 m/s. What is the magnitude of the change in momentum?

Accepted Answer

$$\Delta p = 3.6\ \mathrm{kg\cdot m/s}$$

Momentum and Conservation of Momentum: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards