1. The problem statement, all variables and given/known data For the picture, go to http://s16.photobucket.com/albums/b21/arbilvoldy/pulley.jpg" [Broken]. T1 is for the hanging string with mass m1, and T2 is for the string over the table with mass m2. Two 6.20 kg blocks are connected by a massless string over a pulley of radius 2.40 cm and rotational inertia 7.40x10^-4 kgm^2. The string does not slip on the pulley; it is not known whether there is friction between the table and the sliding block; the pulley's axis is frictionless. When this system is released from rest, the pulley turns through 1.30 rad in 91.0 ms and the acceleration of the blocks is constant. What are (a) the magnitude of the pulley's angular acceleration, (b) the magnitude of either block's acceleration, (c) string tension T1, and (d) string tension T1? 2. Relevant equations The one with which I'm concerned: Torque = FR sin theta 3. The attempt at a solution From drawing free-body diagrams, you get m1g-T1=m1a1 and T2-f2=m2a2 The part I don't get is with getting the net torque on the pulley. The torque is 0 for both the normal force and the weight, that I do know. However, in the student solutions manual, they have the net torque as T1R - T2R = Torque. Why is it that way? Wouldn't the torque from T2 be 0 because the sin of the angle b/w the center of the pulley and the radius is sin0=0?