Question

In the figure, the ball P is released from rest, when the spring is at its natural length. For the block Q of mass $2{{m}_{0}}$ to leave contact with ground at some stage, the minimum mass of P must be

• A. ${{m}_{0}}$
• B. $2{{m}_{0}}$
• C. ${{m}_{0}}/2$
• D. ${{m}_{0}}/4$

Answer 1

Answer: (A)

${{m}_{0}}$

Answer 2

The block will experience maximum upward force, when the ball P is at its lowest position (x). Energy conservation gives $mgx=\frac{1}{2}k{{x}^{2}}$ or $x=2mg/k$ ?(i) For the block Q to leave contact $kx=2\,{{m}_{0}}g$ Solving Eqs. (i) and (ii), we get $m=2{{m}_{0}}/2={{m}_{0}}$