# Chapter Review

### Concept Items

#### 8.1 Linear Momentum, Force, and Impulse

What is impulse?

- Change in velocity
- Change in momentum
- Rate of change of velocity
- Rate of change of momentum

In which equation of Newton’s second law is mass assumed to be constant?

- $\text{F}=ma$
- $\text{F}=\frac{\text{\Delta}\text{p}}{\text{\Delta}t}$
- $\text{F}=\text{\Delta}\text{p}\text{\Delta}t$
- $\text{F}=\frac{\text{\Delta}m}{\text{\Delta}a}$

- $\text{N}$
- $\text{kg}\cdot \text{m}$
- $\text{kg}\cdot \text{m/s}$
- $\text{kg}\cdot {\text{m/s}}^{2}$

What is the equation for linear momentum?

- $\text{p}=m\text{v}$
- $\text{p}=m\text{/}\text{v}$
- $\text{p}=\text{m}{\text{v}}^{2}$
- $\text{p}=\frac{1}{2}\text{m}{\text{v}}^{2}$

#### 8.2 Conservation of Momentum

What is angular momentum?

- The sum of moment of inertia and angular velocity
- The ratio of moment of inertia to angular velocity
- The product of moment of inertia and angular velocity
- Half the product of moment of inertia and square of angular velocity

What is an isolated system?

- A system in which the net internal force is zero
- A system in which the net external force is zero
- A system in which the net internal force is a nonzero constant
- A system in which the net external force is a nonzero constant

#### 8.3 Elastic and Inelastic Collisions

In the equation **p**_{1} + **p**_{2} = **p**'_{1} + **p**'_{2} for the collision of two objects, what is the assumption made regarding the friction acting on the objects?

- Friction is zero.
- Friction is nearly zero.
- Friction acts constantly.
- Friction before and after the impact remains the same.

What is an inelastic collision?

- when objects stick together after impact, and their internal energy is not conserved
- when objects stick together after impact, and their internal energy is conserved
- when objects stick together after impact, and always come to rest instantaneously after collision
- when objects stick together after impact, and their internal energy increases

### Critical Thinking Items

#### 8.1 Linear Momentum, Force, and Impulse

- The first object will acquire more momentum.
- The second object will acquire more momentum.
- Both objects will acquire the same momentum.
- Neither object will experience a change in momentum.

Cars these days have parts that can crumple or collapse in the event of an accident. How does this help protect the passengers?

- It reduces injury to the passengers by increasing the time of impact.
- It reduces injury to the passengers by decreasing the time of impact.
- It reduces injury to the passengers by increasing the change in momentum.
- It reduces injury to the passengers by decreasing the change in momentum.

How much force would be needed to cause a 17 kg ⋅ m/s change in the momentum of an object, if the force acted for 5 seconds?

- 3.4 N
- 12 N
- 22 N
- 85 N

#### 8.2 Conservation of Momentum

A billiards ball rolling on the table has momentum **p**_{1}. It hits another stationary ball, which then starts rolling. Considering friction to be negligible, what will happen to the momentum of the first ball?

- It will decrease.
- It will increase.
- It will become zero.
- It will remain the same.

A ball rolling on the floor with momentum **p**_{1} collides with a stationary ball and sets it in motion. The momentum of the first ball becomes **p**'_{1}, and that of the second becomes **p**'_{2}. Compare the magnitudes of **p**_{1} and **p**'_{2}.

- Momenta
**p**_{1}and**p**'_{2}are the same in magnitude. - The sum of the magnitudes of
**p**_{1}and**p**'_{2}is zero. - The magnitude of
**p**_{1}is greater than that of**p**'_{2}. - The magnitude of
**p**'_{2}is greater than that of**p**_{1}.

Two cars are moving in the same direction. One car with momentum **p**_{1} collides with another, which has momentum **p**_{2}. Their momenta become **p**'_{1} and **p**'_{2} respectively. Considering frictional losses, compare (**p**'_{1} + **p**'_{2} ) with (**p**_{1} + **p**_{2}).

- The value of (
**p**'_{1}+**p**'_{2}) is zero. - The values of (
**p**_{1}+**p**_{2}) and (**p**'_{1}+**p**'_{2}) are equal. - The value of (
**p**_{1}+**p**_{2}) will be greater than (**p**'_{1}+**p**'_{2}). - The value of (
**p**'_{1}+**p**'_{2}) will be greater than (**p**_{1}+**p**_{2}).

#### 8.3 Elastic and Inelastic Collisions

- The first person will gain more velocity as a result of recoil.
- The second person will gain more velocity as a result of recoil.
- Both people will gain the same velocity as a result of recoil.
- The velocity of both people will be zero as a result of recoil.

### Problems

#### 8.1 Linear Momentum, Force, and Impulse

- $1\phantom{\rule{thinmathspace}{0ex}}\text{kg}$
- $2\phantom{\rule{thinmathspace}{0ex}}\text{kg}$
- $5\phantom{\rule{thinmathspace}{0ex}}\text{kg}$
- $250\phantom{\rule{thinmathspace}{0ex}}\text{kg}$

For how long should a force of 130 N be applied to an object of mass 50 kg to change its speed from 20 m/s to 60 m/s?

- 0.031 s
- 0.065 s
- 15.4 s
- 40 s

#### 8.3 Elastic and Inelastic Collisions

If a man with mass 70 kg, standing still, throws an object with mass 5 kg at 50 m/s, what will be the recoil velocity of the man, assuming he is standing on a frictionless surface?

- −3.6 m/s
- 0 m/s
- 3.6 m/s
- 50.0 m/s

- $-0.12\phantom{\rule{thinmathspace}{0ex}}\text{m/s}$
- $0\phantom{\rule{thinmathspace}{0ex}}\text{m/s}$
- $0.12\phantom{\rule{thinmathspace}{0ex}}\text{m/s}$
- $7.5\phantom{\rule{thinmathspace}{0ex}}\text{m/s}$

### Performance Task

#### 8.3 Elastic and Inelastic Collisions

- balls of different weights
- a ruler or wooden strip
- some books
- a paper cup

Make an inclined plane by resting one end of a ruler on a stack of books. Place a paper cup on the other end. Roll a ball from the top of the ruler so that it hits the paper cup. Measure the displacement of the paper cup due to the collision. Now use increasingly heavier balls for this activity and see how that affects the displacement of the cup. Plot a graph of mass vs. displacement. Now repeat the same activity, but this time, instead of using different balls, change the incline of the ruler by varying the height of the stack of books. This will give you different velocities of the ball. See how this affects the displacement of the paper cup.