A uniform metal chain of mass m and length ‘L’ passes over a mass less and frictionless pulley. It is released from rest with a part of its length ’l’ is hanging on one side and rest of its length ‘L-l’ is hanging on oneside and rest of its length ‘L-l’ is hanging on the other side of pulley. At a certain point of time when $l=\frac{L}{x}$  , the acceleration of the chain is $\frac{g}{2}$ . The value of x is