An ideal spring supports a disc of mass M. A body of mass m is released from a certain height from where it falls to hit M. The two masses stick together at the moment they touch and move together from then on . The oscillations reach to a height a above the original level of the disc and depth b blow. it The constant of the force of the spring is

Options

A. `(2mg)/(b-a)`
B. `(mg)/(b-a)`
C. `(2mg)/(a-b)`
D. `(mg)/(2(a-b))`

Answer

C