Question

A block of mass M1 = 0.320 kg is initially at rest on a cart of mass M2 = 0.680 kg with the cart initially at rest on a level air track. The coefficient of static friction between the block and the cart is ?s = 0.610, but there is essentially no friction between the air track and the cart. The cart is accelerated by a force of magnitude F parallel to the air track. Find the maximum value of F that allows the block to accelerate with the cart, without sliding on top of the cart.