Torque acting?

Question

A CD has a mass of 17 g and a radius of 6.0 cm. When inserted into a player, the CD starts from rest and accelerates to an angular velocity of 21 rad/s in 0.74 s. Assuming the CD is a uniform solid disk, determine the net torque acting on it.

Answer 1

The formula for torque, T (tau), is
T = I*alpha
where I is the rotational inertia and alpha is roatational acceleration in radians/second^2.
(This formula is the equivalent, for rotational situations, of F = m*a.) To get alpha, w = alpha*t where w is your 21 rad/s.

For a disk, I = (1/2)*M*R^2