Question

When a rigid object rotates about a fixed axis, what is true about all the points in the object? (There could be more than one correct choice.)
A) they all have the same tangential speed
B) they all have the same tangential acceleration
C) they all have the same angular speed
D) they all have the same angular acceleration

Answer 1

Answer:

C) they all have the same angular speed  

D) they all have the same angular acceleration

Explanation:

Wrong --> they all have the same tangential speed. The points close to the axis will have less speed than the points away from the axis.

Wrong --> they all have the same tangential acceleration. Similarly, the points close to the axis will have smaller acceleration than the points away from the axis.

Correct --> they all have the same angular speed. Angular speed is the same for all the particles in the rotating object.

Correct --> they all have the same angular acceleration. Angular acceleration is the same for all the particles in the rotating object.

This all comes from the following relations:

v = ωR

a = αR

where ω is the angular velocity and α is the angular acceleration.

As can be seen from above, tangential velocity and acceleration depends on the distance from the axis, whereas the angular velocity and acceleration is the same for all the points on the rotating body.