In the figure, block A is released from rest when the spring is its natural length for the block B of mass m to leave contact with the ground at some stage what should be the minimum mass of block A?
.

Options

A. 2M
B. M
C. M/2
D. A function of M and the force constant of the spring

Answer

C

Explanation

Let m be minimum mass of ball.
Let mass A moves downwards by x.
From conservation of energy.
`mgx=1/2kx^(2)`
`x=((2mg)/k)`
For mass M to leave contact with ground
`kx=mg`
`k((2mg)/k)=Mg`
`m=M/2`