Question

A block of mass $m$ is kept on a platform. Platform starts moving upwards with an acceleration of $\frac{g}{2}$ . Find the work done by the normal force on the block in the first one second.

• A. $\frac{3 \, m g^{2}}{2}$
• B. zero
• C. $\frac{3 m g^{2}}{8}$
• D. $\frac{3 m g^{2}}{4}$

Answer 1

Answer: (C)

$N-mg=\frac{m g}{2}$
$N=\frac{3 m g}{2}$
$s=ut+\frac{1}{2}at^{2}$
$=0+\frac{1}{2}\frac{g}{2}\left(1\right)^{2} \, $
$=\frac{g}{4}$
$W_{N}=\frac{3 m g}{2}\times \frac{g}{4}$
$=\frac{3 m g^{2}}{8}=\frac{3 m g^{2}}{8}$