Question

A mass $M$ is lowered with the help of a string by a distance $x$ at a constant acceleration $g/2$. The work done by the string will be

• A. $Mgx$
• B. $-\frac{Mgx}{2}$
• C. $\frac{1}{2}Mg{x}^2$
• D. $Mg{x}^2$

Answer 1

The correct option is B $-\frac{Mgx}{2}$

[B] Let tension in string be T, mass = M

$Mg-T=\frac{Mg}{2}\Rightarrow T=\frac{Mg}{2}$

work done by string

$\begin{array}{c}\frac{Mg}{2}\times x\times \frac{\cos }{80}\\ =\frac{-Mgx}{2}\end{array}$