A grindstone in the shape of a solid disk with diameter 0.510 and a mass of m= 50.0kg is rotating at w = 900rev/min. You press an ax against the rim with a normal force of N= 160N, and the grindstone comes to rest in 7.00sec. Find the coefficient of friction between the ax and the grindstone. You can ignore friction in the bearings. ---- Simply put, I have no idea how to connect the information here to Coefficient of friction. I have found Torque using t = I*(Angular Acceleration) Where Moment of Inertia = 1/2 MR^2 = 1.63kg*m^2 And Angular Acceleration was found using w = w(initial) + angular acceleration*t. I found the angular acceleration to be -2.14 rev/sec^2 (I converted the angular velocity to rev/sec in finding this). And torque was equal to -3.5N... I have all this info so far, but have no idea how to connect it to Coefficient of Friction, I thought maybe there would be some ratio with the Normal Force, but I don't have Friction Force so I'm pretty much stuck... Any help would be greatly appreciated. -L.