an electric fan is turned off, and its angular velocity decreases uniformly from 500.0 rev/min to 200.0 rev/min in 4.00 s. (a) find the angular acceleration in rev/s2 and the number of revolutions made by the motor in the 4.00 s interval. (b) how many more seconds are required for the fan to come to trest if the angular acceleration remains constant at the value calculated in part (a)?