A block of mass m shown in figure is in equilibrium. If it is displaced downward further by x and released find its acceleration just after it is released. Take pulleys to be light and smooth and strings light.

Initially the block is at rest action of force 2T upward and mg downwards. When the block is pulled downwards by x, the spring extends by 2x. Hence tension T increases by 2kx. Thus the net unbalanced force on block of mass m is 4kx.∴ Acceleration of the block = 4kxm