Question 1

A driver makes direct contact with a steering wheel during a 35 mph crash and comes to rest in about $$\Delta t = 0.05\ \mathrm{s}. If$$, instead, the driver makes contact with an air bag and comes to rest in about $$\Delta t = 0.2\ \mathrm{s}$$, what is the ratio $$\dfrac{F_{	ext{air bag}}}{F_{	ext{wheel}}} of $$the force exerted by the air bag to the force exerted by the steering wheel, assuming the change in momentum is the same in both cases?

Accepted Answer

$$0.25$$

Question 2

Which of the following best explains why air bags reduce injuries in car crashes?

Accepted Answer

They increase the time over which the momentum of the driver changes, thereby reducing the average force.

Question 3

A $$1.50\ \mathrm{kg}$$ block slides down a frictionless track from a height $$h$$ and collides elastically with a $$2.10\ \mathrm{kg}$$ block at rest. If $$h = 0.61\ \mathrm{m}$$, what is the speed of the $$1.50\ \mathrm{kg}$$ block just before the collision?

Accepted Answer

$$3.46\ \mathrm{m/s}$$

Question 4

In an elastic collision between two blocks of masses $$m_1$$ and $$m_2$$, with $$m_1$$ moving and $$m_2 at $$rest, which of the following is always conserved?

Accepted Answer

Both kinetic energy and momentum

Question 5

After the elastic collision described in the study material, what is the velocity of the $$2.10\ \mathrm{kg}$$ block immediately after the collision? (Assume $$m_1 = 1.50$$\ \mathrm{kg}$$, m_2$ = 2.10\ \mathrm{kg}$$, $$v_{1i} = 3.46\ \mathrm{m/s}$$, $$v_{2i} = 0.)$$

Accepted Answer

$$2.00\ \mathrm{m/s}$$

Question 6

Which equation correctly expresses the conservation of momentum for the two-block collision described?

Accepted Answer

$$m_1 v$$_{1i} + $$m_2 v$$_{2i} = $$m_1 v$$_{1f} + $$m_2 v$$_{2f}$$

Question 7

If the collision between the two blocks were perfectly inelastic, what would be the final velocity of the combined mass after the collision? (Use $$m_1 = 1.50$$\ \mathrm{kg}$$, m_2$ = 2.10\ \mathrm{kg}$$, $$v_{1i} = 3.46\ \mathrm{m/s}$$, $$v_{2i} = 0.)$$

Accepted Answer

$$1.36\ \mathrm{m/s}$$

Question 8

A $$70\ \mathrm{kg}$$ driver comes to rest from $$15.6\ \mathrm{m/s} in$$ $$0.05\ \mathrm{s}$$ during a crash. What is the average force exerted on the driver?

Accepted Answer

$$21,840\ \mathrm{N}$$

Question 9

Which of the following statements about elastic and inelastic collisions is correct?

Accepted Answer

In elastic collisions, both momentum and kinetic energy are conserved; in inelastic collisions, only momentum is conserved.

Question 10

A $$1.50\ \mathrm{kg}$$ block slides down a frictionless track from a height $$h$$ and collides elastically with a $$2.10\ \mathrm{kg}$$ block at rest. If the collision is perfectly elastic, which formula gives the final velocity of the $$1.50\ \mathrm{kg}$$ block after the collision?

Accepted Answer

$$v_{1f} = \dfrac{m_1$ - m_2$}{m_1$ + m_2$} v_{1i}$$

Question 11

If the time to stop is doubled in a collision (with the same change in momentum), what happens to the average force experienced?

Accepted Answer

It is halved.

Question 12

A $$1.50\ \mathrm{kg}$$ block slides down a frictionless track from a height $$h = 0.61\ \mathrm{m}. $$What is the kinetic energy of the block just before it collides with the $$2.10\ \mathrm{kg}$$ block at rest?

Accepted Answer

$$8.97\ \mathrm{J}$$

Question 13

Which of the following best describes the impulse experienced by the driver during the crash?

Accepted Answer

It is equal to the change in momentum of the driver.

Question 14

A $$1.50\ \mathrm{kg}$$ block moving at $$3.46\ \mathrm{m/s}$$ collides elastically with a $$2.10\ \mathrm{kg}$$ block at rest. What is the final velocity of the $$1.50\ \mathrm{kg}$$ block after the collision?

Accepted Answer

$$-0.57\ \mathrm{m/s}$$

Question 15

Which of the following real-world scenarios best illustrates the principle of impulse-momentum?

Accepted Answer

A baseball player following through with a swing to increase the time of contact with the ball.

Chapter 9: Linear Momentum & Collisions – Example Problems Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards