A pulley of radius 2 m is rotated about its axis by a force F =20t-5t2 newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kgm2, the number of rotations made by the pulley before its direction of motion it reversed, is
(a) more than 6 but less than 9
(b) more than 9
(c) less than 3
(d) more than 3 but less than 6