Question

In the figure, the ball A is released from rest when the spring is at its natural (unstretched) 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. 2M
• B. M
• C. $\frac { M } { 2 }$
• D. A function of M and the force constant of the spring

Answer 1

Answer: (C)

$\frac { M } { 2 }$

Answer 2

The spring will exert the maximum force when the ball is at its lowest position. If the ball has descended through a distance x to reach this position, mgx = $\frac { 1 } { 2 }$ kx². For the block B to leave contact, spring force = kx = Mg.