1. The problem statement, all variables and given/known data Block B, with mass 5.00kg, rests on block A, with mass 8.00kg , which in turn is on a horizontal tabletop. There is no friction between block A and the tabletop, but the coefficient of static friction between block A and block B is 0.750. A light string attached to block A passes over a frictionless, massless pulley, and block C is suspended from the other end of the string. What is mass of block C? 2. Relevant equations F=ma FFriction = μmg 3. The attempt at a solution I made equations for all 3 masses: box C: mCa=mcg-T. box B: mBa=FS box A: mAa=T-FS added all three equations, the internal forces (tension and friction) cancel and I get: mCg = a(mA+mB+mC) However I still have 2 unknowns ([itex]a[/itex] and mc) I attempted to figure out acceleration using the equation for box B: mBa=FS mBa=μmBg a = μg a = (0.750)(9.8) a = 7.35 m/s^2 but that seems to be a sketchy way to do it?