1. The problem statement, all variables and given/known data A string passing over a pulley has a 3.8-kg mass hanging from one end and a 3.15-kg mass hanging from the other end. The pulley is a uniform solid cylinder of radius 4.0 cm and mass .80 kg. (a) If the bearings of the pulley were frictionless, what would be the acceleration of the two masses? (b) In fact, it is found that if the heavier mass is given a downward speed of .2 m/s, it comes to rest in 6.2 s. What is the average frictional torque acting on the pulley? 2. Relevant equations I= .5*M*R^2 For mass 1: F_1 - (m_1g) = m_1a For mass 2: m_2g - F_2 = m_2a 3. The attempt at a solution The inertia for the pulley is simple. .5*.8*.04^2 = .00064 Now, rearranging the first two equations: a= (F_1 - m_1g)/(m_1) a=(m_2g-F_2)/(m_2) Since the magnitude of the acceleration has to be the same for both masses... And now is where I am stuck. I have 3 unknowns (F_1, F_2, a), and the Inertia equation times alpha can be equivalent to (F_2 - F_1)*r. But, that introduces alpha into the mix, which would be another unknown. What am I missing? Any help is greatly appreciated!