Determine net torque?

Question

CD has mass of 17 grams 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 0.95 seconds.

Answer 1

Torque =(moment of inertia )x(angular acceleration )

moment of inertia= .5 m r^2
moment of inertia= .5 (.017)(.06)^2=0.0000306 kg m^2

angular acceleration = (change in angular velocity )/(change in time)

angular acceleration=( 21-0)/(.95-0)=22.1 rad/sec^2

Torque=(0.0000306)(22.1)=6.7626 E-4 N m