Question

In the figure ball A is released from rest, when the spring is at its natural length. For the block B of mass M to leave contact with the ground at some stage, the minimum mass of A must be

• A. 2 M
• B. M
• C. $\frac{M}{2}$
• D. A function of M and force constant of spring

Answer 1

The correct option is C

$\frac{M}{2}$

For B
Just to loose contact
$Mg=Kx\Rightarrow x=\frac{Mg}{K}$
Applying WET
$W{E}_e+W{D}_s=\Delta KE\Rightarrow -\frac{1}{2}K{x}^2+mgx=0\Rightarrow m=\frac{M}{2}$