Question

Two blocks with masses M1=8.50kg and M2=1.40kg are attached by a thin string which goes over a frictionless, massless pulley. M1 slides on an incline and there is friction between M1 and the incline. The incline is at an angle of 23.0 degrees from horizontal. M2 travels down at a constant velocity of 0.91m/s. Calculate the magnitude of the frictional force acting on M1.