AB is a vertically suspended elastic cord of negligible mass and length L. Its force constant is `k=(4mg)/L`. There is a massless platform attached to the lower end of the cord. A monkey of mass m starts from top end A and slides down the cord with a uniform acceleration of `g/2` . Just before landing on the platform, the monkey loses grip on the cord. After landing on the platform the monkey stays on it. Calculate the maximum extension in the elastic cord.