A block of mass is placed against the vertical front of a cart of mass as shown in (Figure 1). Assume that the cart is free to roll without friction and that the coefficient of static friction between the block and the cart is μs. Derive an expression for the minimum horizontal force that must be applied to the block in order to keep it from falling to the ground. Express your answer in terms of acceleration of gravity and some or all of the variables m ,M, and μs.