1. The problem statement, all variables and given/known data This figure shows a uniform disk, with mass M = 2.5 kg and radius R = 20 cm, mounted on a fixed horizontal axle. A block with mass m = 1.2 kg hangs from a massless cord that is wrapped around the rim of the disk. Sample problem 10-8 (has picture diagram and detailed solution): http://astro1.panet.utoledo.edu/~mheben/PHYS_2130/Chapter11-1_mh.pdf 2. Relevant equations T – mg = ma torque = I α -RT ??? = (1/2)MR^2 α a = a(subscript t) = α R 3. The attempt at a solution I understand how to do the problem but what I don't understand is how they got -RT. Torque is FrSin(theta) and the sin of 90 degrees is 1 not -1 so I would really appreciate any insight on how they got -RT.