Question 1

A 0.10 kg tennis ball strikes a racket at 20 m/s and rebounds at 15 m/s in the opposite direction. What is the magnitude of the impulse delivered to the ball by the racket?

Accepted Answer

$$3.5\ \mathrm{kg\cdot m/s}$$

Question 2

Which of the following statements best explains why airbags reduce injuries in car accidents?

Accepted Answer

Airbags increase the time over which the momentum changes, reducing the average force.

Question 3

A 1.5 kg soccer ball is kicked from rest to a speed of 12 m/s by a constant force over 0.10 s. What is the average force applied to the ball?

Accepted Answer

$$F_{\mathrm{avg}} = \frac{\Delta p}{\Delta t} = \frac{(1.5\ \mathrm{kg})(12\ \mathrm{m/s})}{0.10\ \mathrm{s}} = 180\ \mathrm{N}$$

Question 4

A 60 kg student jumps off a table and lands with bent knees, increasing the time of contact with the ground to 0.10 s. If the student lands stiff-legged, the time of contact is only 0.01 s. Assuming the change in momentum is the same in both cases, how does the average force compare?

Accepted Answer

The average force is 10 times greater when landing stiff-legged.

Question 5

Which of the following is the correct SI unit for impulse?

Accepted Answer

$$\mathrm{kg\cdot m/s}$$

Question 6

A 1500 kg car crashes into a wall and comes to rest from 15 m/s in 0.15 s. What is the magnitude of the average force exerted by the wall on the car?

Accepted Answer

$$F_{\mathrm{avg}} = \frac{(1500\ \mathrm{kg})(17.6\ \mathrm{m/s})}{0.15\ \mathrm{s}} = 1.76 	imes 10^5$\ \mathrm{N}$$

Question 7

Which of the following best describes the impulse-momentum theorem?

Accepted Answer

The impulse on an object is equal to the change in its momentum.

Question 8

A 2.0 kg object moving to the right at 0.50 m/s experiences a constant force of 2.0 N to the right for 0.5 s. What is its final speed?

Accepted Answer

$$v_f = 1.0\ \mathrm{m/s}$$

Question 9

During a collision, the area under the force vs. time curve represents:

Accepted Answer

The impulse delivered to the object.

Question 10

A 1.0 kg ball moving at 2.0 m/s perpendicular to a wall rebounds at 1.5 m/s in the opposite direction. What is the change in momentum of the ball?

Accepted Answer

$$3.5\ \mathrm{N\cdot s}$$\ away\ from\ wall

Question 11

Which of the following scenarios will result in the largest average force on an object, assuming the same change in momentum in each case?

Accepted Answer

A large force acting over a short time.

Question 12

A karate expert splits a stack of bricks by bringing her hand down swiftly. Why is the force of impact so large?

Accepted Answer

Because the time interval of contact is very short.

Question 13

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

Accepted Answer

Impulse is always positive.

Question 14

A 0.5 kg ball is initially at rest. A player kicks it, applying an average force of 50 N for 0.04 s. What is the final speed of the ball?

Accepted Answer

$$v_f = 5.0\ \mathrm{m/s}$$

Question 15

Which of the following best explains why landing on a pillow hurts less than landing on concrete?

Accepted Answer

The pillow increases the time over which your momentum changes, reducing the average force.

Question 16

A 0.2 kg baseball is hit by a bat and changes velocity from 10 m/s toward the pitcher to 20 m/s away from the pitcher. What is the impulse delivered by the bat?

Accepted Answer

$$J = 0.2\ \mathrm{kg} 	imes (20\ \mathrm{m/s} - (-10\ \mathrm{m/s})) = 6.0\ \mathrm{kg\cdot m/s}$$

Question 17

Which of the following is a real-world application of the impulse-momentum theorem?

Accepted Answer

Wearing padded gloves in boxing to increase the time of impact and reduce the force on the hand.

Question 18

If the net external force on a system is zero, what can be said about the system's total linear momentum?

Accepted Answer

It remains constant.

Question 19

A 0.45 kg soccer ball is kicked from rest to a speed of 18 m/s. What is the impulse imparted to the ball?

Accepted Answer

$$J = (0.45\ \mathrm{kg})(18\ \mathrm{m/s}) = 8.1\ \mathrm{N\cdot s}$$

Impulse and Momentum: Concepts, Applications, and Problem Solving

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