1. The problem statement, all variables and given/known data M1 and M2 are two masses connected as shown. The pulley is light (massless) and frictionless. Find the mass M1, given that M2 (3.5 kg) accelerates downwards at 3.35 m/s^2, θ is 35o, and μk is 0.25. http://img525.imageshack.us/img525/7076/prob31fricpullplaneyi0.gif [Broken] 2. Relevant equations 3. The attempt at a solution The total force (which is the total mass times the acceleration) is equal to the sum of the forces. Forces: Gravity = M1g Normal = M1g(sinθ) Applied = M1a Kinetic Friction = μkM1a g=9.81m/s^2 a(M1 + M2) = -M1g +M1g(sinθ) +M1a -μkM1a M1a +M2a = M1g((sinθ)-1) +M1a -μkM1a M2a = M1(g((sinθ)-1) -μka) M1 = M2a/(g((sinθ)-1) -μka) M1 = (3.5*3.35)/(9.81((sin35)-1) -0.25*3.35) M1 = 11.725/(9.81(-.426)-0.8375) M1 = -2.34 kg A negative answer isn't even possible, but I tried putting in "2.34 kg" is an answer and that didn't work. I don't know what I'm doing wrong.