Question

A mass M is lowered with the help of a string by a distance h at a constant acceleration $\frac{g}{2}$. The work done by string will be

• A. $\frac{Mgh}{2}$
• B. $-\frac{Mgh}{2}$
• C. $\frac{3Mgh}{2}$
• D. $-\frac{3Mgh}{2}$

Answer 1

The correct option is B

$-\frac{Mgh}{2}$

Tension in the string,

$T=M(g-a)=M(g-\frac{g}{2})=Mg/2$

$W=Force\times Displacement=-\frac{Mgh}{2}$

Negative sign is because tension is in the upward direction and displacement is in the downward direction.