A ball of mass m falls freely from rest. When it has reached a speed v, it strikes a vertical spring. The spring is compressed by distance y before the ball moves upwards again. Assume that all the energy the ball loses becomes elastic potential energy in the spring. What is the average force exerted by the spring during its compression?
Amv2/2y
Bm/2y (v2-2gy)
Cmv2/y
Dm/2y (v2+2gy)