A grindstone is rotating uniformly at 420 rpm when its motor is switched off. The stone comes to rest 28 s after the motor is cut.
(a) Convert the initial angular speed of 420 rpm into rad s−1.
(b) Assuming constant angular retardation, find the magnitude of the angular acceleration while the stone is slowing down.
(c) How many complete revolutions does the grindstone make before coming to rest?