Question

A string is used to pull a block of mass $m$ vertically up by a distance $h$ at a constant acceleration $\frac{g}{4}$. The work done by the tension in the string is

• A. $+\frac{3}{4}mgh$
• B. $-\frac{1}{4}mgh$
• C. $+\frac{5}{4}mgh$
• D. $+mgh$

Answer 1

The correct option is C $+\frac{5}{4}mgh$

Applying Newton's $2^{nd}$ law on mass $m$,
$T-mg=ma$

$T=m(g+a)=m(g+\frac{g}{4})=\frac{5}{4}mg$
Work done by the string is
$W_{string}=T.h=\frac{5}{4}mgh$