Question

A cord is used to lower vertically a block of mass $M$ by a distance $d$ with constant downword acceleration $\frac{g}{2}$ work done by the cord on the block is

• A. $\frac{-Mgd}{2}$
• B. $\frac{Mgd}{4}$
• C. $\frac{-3Mgd}{4}$
• D. $Mgd$

Answer 1

The correct option is A $\frac{-Mgd}{2}$

Work done$=F.s=\left(M\frac{g}{2}\right)d$

Here we are asked the work done by the cord on the block. So a negative sign will come as the tension force will develop in the upward direction in the cord and the displacement is in downward direction

Hence correct answer is option $A$