1. The problem statement, all variables and given/known data A string passing over a pulley has a 3.80 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 0.04 m and mass 0.80 kg. It is found that if the heavier mass is give a downward speed of 0.20 m/s, it comes to rest in 6.2 s. What is the average frictional torque acting on the pulley? 2. Relevant equations T = F*r F = ma T = I* alpha 3. The attempt at a solution Newton's second law for masses: FTA - mag= ma*a (the heavier one) mb*g -FTB = mb*a For the pulley: FTB*rpulley(ccw-positive) - FTA*rpulley(cw-negative) + (+-_____ )= I*alpha The pulley is rotating ccw, so I thought I had to write minus friction because the friction must be opposite of rotation direction, but then saw this and got really confused. https://www.physicsforums.com/threa...que-acting-on-the-pulley.232961/#post-1716480 Determining the sign of frictional torque in this equation, should it be positive or negative?