A disk rotates about its central axis starting from rest and accelerates with constant angular acceleration. At one time it is rotating at 10 rev/s; 60 revolutions later, its angular speed is 15 rev/s. Calculate

(a) The angular acceleration,

(b) The time required to complete the 60 revolutions,

(c) The time required to reach the 10 rev/s angular speed, and

(d) The number of revolutions from rest until the time the disk reaches the 10 rev/s angular speed.