13-51. The block A has a mass mA and rests on the pan B,which has a mass mg. Both are supported by a spring having a stiffness k that is

attached to the bottom of the pan and to the ground. Determine the distance d the pan should be pushed down from the equilibrium position and then released from rest so that separation of the block will take place from the surface of the pan at the instant the spring becomes unstretched.