# AP Physics C: Mechanics : Understanding Linear-Rotational Equivalents

## Example Questions

### Example Question #1 : Understanding Linear Rotational Equivalents

What is the rotational equivalent of mass?

Moment of inertia

Torque

Angular momentum

Moment of inertia

Explanation:

The correct answer is moment of inertia. For linear equations, mass is what resists force and causes lower linear accelerations. Similarly, in rotational equations, moment of inertia resists torque and causes lower angular accelerations.

### Example Question #41 : Mechanics Exam

In rotational kinematics equations, what quantity is analogous to force in linear kinematics equations?

Angular acceleration

Moment of inertia

Torque

Impulse

Torque

Explanation:

Just as force causes linear acceleration, torque causes angular acceleration. This can be seen most in the linear-rotational comparison of Newton's second law:

### Example Question #1 : Rotational Motion And Torque

A boot is put in a  stick which is attached to a rotor. The rotor turns with an angular velocity of . What is the linear velocity of the boot?

Explanation:

Linear (tangential) velocity,  is given by the following equation:

Here,  is the angular velocity in radians per second and  is the radius in meters.

Solve.

### Example Question #1 : Understanding Linear Rotational Equivalents

A particle is moving at constant speed in a straight line past a fixed point in space, c. How does the angular momentum of the particle about the fixed point in space change as the particle moves from point a to point b?

The angular momentum decreases

The angular momentum increases

The angular momentum does not change

It cannot be determined without knowing the mass of the particle

The particle does not have angular momentum since it is not rotating