Answer:
Two equal and opposite parallel forces not acting along the same line, form a couple. A couple is always needed to produce the rotation.
For example, turning a key in a lock and turning a steering wheel.
The distance between two particles that are <em>in phase</em>
Answer: The radial acceleration of a point on the rim in two ways is 13.20 m/s^2
Explanation: Please see the attachments below