A 2.0 kg, 30-cm-diameter disk is spinning at 300 rpm. How much friction force must the brake apply to the rim to stop it in 3.0 s?
The moment of inertia of the disk is 0.5mr^(2), where m is the mass and r the radius of the disk. Find the torque needed for the (negative) acceleration using the moment of inertia, and find the force by the definition of torque.