Agrindstone, initially at rest, is given a constant angular acceleration so that it makes 20.0 rev in the first 8.00 s. what is its angular acceleration?

The angle covered by the grindstone during this time is, converting into radians,


This is a rotational motion with constant angular acceleration , and with initial angular speed . The angle covered in a time t is given by

because the initial angular speed is zero.
Using t=8.00 s, we can find the value of angular acceleration: