### Concept Items

### 6.1 Angle of Rotation and Angular Velocity

1.

One revolution is equal to how many radians? Degrees?

- $1\phantom{\rule{thinmathspace}{0ex}}\text{rev}=\pi \phantom{\rule{thinmathspace}{0ex}}\text{rad}={180}^{\circ}$
- $1\phantom{\rule{thinmathspace}{0ex}}\text{rev}=\pi \phantom{\rule{thinmathspace}{0ex}}\text{rad}={360}^{\circ}\phantom{\rule{negativethinmathspace}{0ex}}$
- $1\phantom{\rule{thinmathspace}{0ex}}\text{rev}=2\pi \phantom{\rule{thinmathspace}{0ex}}\text{rad}={180}^{\circ}\phantom{\rule{negativethinmathspace}{0ex}}$
- $1\phantom{\rule{thinmathspace}{0ex}}\text{rev}=2\pi \phantom{\rule{thinmathspace}{0ex}}\text{rad}={360}^{\circ}$

2.

What is tangential velocity?

- Tangential velocity is the average linear velocity of an object in a circular motion.
- Tangential velocity is the instantaneous linear velocity of an object undergoing rotational motion.
- Tangential velocity is the average angular velocity of an object in a circular motion.
- Tangential velocity is the instantaneous angular velocity of an object in a circular motion.

3.

What kind of motion is called *spin*?

- Spin is rotational motion of an object about an axis parallel to the axis of the object.
- Spin is translational motion of an object about an axis parallel to the axis of the object.
- Spin is the rotational motion of an object about its center of mass.
- Spin is translational motion of an object about its own axis.

### 6.2 Uniform Circular Motion

4.

What is the equation for centripetal acceleration in terms of angular velocity and the radius?

- ${a}_{c}=\frac{{\omega}^{2}\phantom{\rule{negativethinmathspace}{0ex}}}{r}$
- ${a}_{c}=\frac{\omega}{r}$
- ${a}_{c}=r{\omega}^{2}\phantom{\rule{negativethinmathspace}{0ex}}$
- ${a}_{c}=r\omega \phantom{\rule{negativethinmathspace}{0ex}}$

5.

How can you express centripetal force in terms of centripetal acceleration?

- ${F}_{c}=\frac{{a}_{c}^{2}\phantom{\rule{negativethinmathspace}{0ex}}}{m}$
- ${F}_{c}=\frac{{a}_{c}}{m}$
- ${F}_{c}=m{a}_{c}^{2}\phantom{\rule{negativethinmathspace}{0ex}}$
- ${F}_{c}=m{a}_{c}$

6.

What is meant by the word centripetal?

- center-seeking
- center-avoiding
- central force
- central acceleration

### 6.3 Rotational Motion

7.

Conventionally, for which direction of rotation of an object is angular acceleration considered positive?

- the positive
*x*direction of the coordinate system - the negative
*x*direction of the coordinate system - the counterclockwise direction
- the clockwise direction

8.

When you push a door closer to the hinges, why does it open more slowly?

- It opens slowly, because the lever arm is shorter so the torque is large.
- It opens slowly because the lever arm is longer so the torque is large.
- It opens slowly, because the lever arm is shorter so the torque is less.
- It opens slowly, because the lever arm is longer so the torque is less.

9.

When is angular acceleration negative?

- Angular acceleration is the rate of change of the displacement and is negative when $\omega $ increases.
- Angular acceleration is the rate of change of the displacement and is negative when $\omega $ decreases.
- Angular acceleration is the rate of change of angular velocity and is negative when $\omega $ increases.
- Angular acceleration is the rate of change of angular velocity and is negative when $\omega $ decreases.