Q: A tennis player hits a 57 g ball with a force of 560 N for 0.0050 s. What is the speed of the ball as it leaves the racket?

49.1 m/s $$v = \frac{F \Delta t}{m} = \frac{560 \times 0.0050}{0.057} = 49.1 m/s$$

Q: A 60-kg person lands straight-legged and comes to a halt in 0.02 s. What is the average force exerted by the ground on the person?

29,400 N $$F = \frac{m \Delta v}{\Delta t} = \frac{60 \times 9.8}{0.02} = 29,400 N$$

Q: A 75 kg boxer punches a heavy bag at 8 m/s and stops in 0.02 s. What is the average force exerted on the bag?

30,000 N $$F = \frac{m \Delta v}{\Delta t} = \frac{75 \times 8}{0.02} = 30,000 N$$

Question 1

A 50.0 kg person pushes off a 5.0 kg skateboard and moves to the left at 0.600 m/s. What is the speed and direction of the skateboard immediately after the push, assuming no external forces act on the system?

Accepted Answer

The skateboard moves to the right at 6.00 m/s. $$v_{skateboard} = \frac{m_{person}}{m_{skateboard}} v_{person} = \frac{50.0}{5.0} 	imes 0.600 = 6.00 m/s$$

Question 2

Which of the following best describes the law of conservation of linear momentum?

Accepted Answer

The total linear momentum of a system remains constant if no external forces act.

Question 3

Two ice hockey players collide and stick together. Player A (80.0 kg) moves at 5.00 m/s to the right, and Player B (80.0 kg) is at rest. What is their velocity after the collision?

Accepted Answer

2.50 m/s to the right

Question 4

Which equation correctly expresses the linear momentum $$p of an $$object with mass $$m$$ and velocity $$v$$?

Accepted Answer

$$p = m v$$

Question 5

A 1.5 × $$10^3 kg $$car moving north at 35.0 m/s collides head-on with a 7.50 × $$10^3 kg $$truck moving south at 25.0 m/s. If they stick together after the collision, what is their velocity and direction?

Accepted Answer

South at 15.0 m/s. $$v = \frac{m_{car} v_{car} + m_{truck} v_{truck}}{m_{car} + m_{truck}} = \frac{(1.5 	imes 10^3$ 	imes 35.0) + (7.5 	imes 10^3$ 	imes (-25.0))}{1.5 	imes 10^3$ + 7.5 	imes 10^3$} = -15.0 m/s$$

Question 6

Which of the following is true for an elastic collision?

Accepted Answer

Both total momentum and total kinetic energy are conserved.

Question 7

A tennis player hits a 57 g ball with a force of 560 N for 0.0050 s. What is the speed of the ball as it leaves the racket?

Accepted Answer

49.1 m/s $$v = \frac{F \Delta t}{m} = \frac{560 	imes 0.0050}{0.057} = 49.1 m/s$$

Question 8

Which scenario best describes a completely inelastic collision?

Accepted Answer

Two cars collide and stick together after the collision.

Question 9

If the net external force on a system is zero, what happens to the system's total momentum?

Accepted Answer

It remains constant.

Question 10

A 60-kg person lands straight-legged and comes to a halt in 0.02 s. What is the average force exerted by the ground on the person?

Accepted Answer

29,400 N $$F = \frac{m \Delta v}{\Delta t} = \frac{60 	imes 9.8}{0.02} = 29,400 N$$

Question 11

Which of the following is a vector quantity?

Accepted Answer

Linear momentum

Question 12

In a 1D elastic collision between two objects of equal mass, where one is initially at rest, what happens to their velocities after the collision?

Accepted Answer

The moving object stops and the stationary object moves with the initial velocity.

Question 13

A 75 kg boxer punches a heavy bag at 8 m/s and stops in 0.02 s. What is the average force exerted on the bag?

Accepted Answer

30,000 N $$F = \frac{m \Delta v}{\Delta t} = \frac{75 	imes 8}{0.02} = 30,000 N$$

Question 14

Which of the following statements about momentum and kinetic energy is correct?

Accepted Answer

Objects with the same momentum can have different kinetic energies.

Question 15

A 1.60 kg block moving right at 4.00 m/s collides elastically with a 2.10 kg block moving left at 2.51 m/s. What is the velocity of the 1.60 kg block after the collision?

Accepted Answer

−0.60 m/s to the left (using conservation of momentum and energy)

Question 16

During a collision, the product of the force acting on an object and the duration over which that force acts is called:

Accepted Answer

Impulse

Question 17

A rock of mass $$m$$ falls freely under gravity for time $$t. $$What is its momentum as a function of time?

Accepted Answer

$$p = m g t$$

Question 18

Why do tennis players follow through after hitting the ball?

Accepted Answer

To increase the time of contact and thus increase the impulse delivered to the ball.

Question 19

In a two-dimensional collision, which components of momentum are conserved if no external forces act?

Accepted Answer

Both x- and y-components

Question 20

A bouncy rubber ball and a clay ball of equal mass are dropped from the same height. Which experiences a greater change in momentum upon hitting the ground?

Accepted Answer

The rubber ball, because it bounces back.

Chapter 8: Linear Momentum and Collisions – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards