Exam

JEE Main

Year

2019

Date

10 January

Shift

Morning Shift

Subject

Physics

Chapter

Laws of Motion

JEE Main 2019 · 10 January · Morning Shift · Physics · Laws of Motion

A block of mass m is kept on a platform which starts from rest with...

A block of mass $m$ is kept on a platform which starts from rest with a constant acceleration $g / 2$ upwards, as shown in the figure. Work done by normal reaction on block in time $t$ is

Step-by-step solution

$N - mg = \dfrac{mg}{2}$
$N = \dfrac{3mg}{2}$
$s = ut + \dfrac{1}{2}a{t}^{2}$
$= 0 + \dfrac{1}{2}\dfrac{g}{2}{t}^{2}$
$= \dfrac{g}{4}$${t}^{2}$
${W}_{N} = \dfrac{3mg}{2} \times \dfrac{g}{4}{t}^{2}$
$= \dfrac{3m{g}^{2}{t}^{2}}{8} = \dfrac{3m{g}^{2}{t}^{2}}{8}$