The open-link chain of total length L and of mass ρ per unit length is released from res...

The open-link chain of total length L and of mass ρ per unit length is released from rest at x = 0 at the same instant that the platform starts from rest at y = 0 and moves vertically up with a constant acceleration a. Determine the expression for the total force R exerted on the platform by the chain t seconds after the motion starts.