JEE Main 202120 JulyMorning Shift

Exam: JEE Main
Year: 2021
Date: 20 July
Shift: Morning Shift
Subject: Physics
Chapter: Center of Mass, Momentum and Collision

JEE Main 2021 · 20 July · Morning Shift · Physics · Center of Mass, Momentum and Collision

A body having specific charge 8μ C g ^ - 1 is resting on a...

A body having specific charge $8\mu C{g}^{- 1}$ is resting on a frictionless plane at a distance $10cm$ from the wall (as shown in the figure). It starts moving towards the wall when a uniform electric field of $100V{m}^{- 1}$ is applied horizontally towards the wall. If the collision of the body with the wall is perfectly elastic, then the time period of the motion will be $____s .$

A body having specific charge 8μ C g ^ - 1 is resting on a frictionless plane at a distance 10cm from the wall (as

Correct answer

Step-by-step solution

A body having specific charge 8μ C g ^ - 1 is resting on a frictionless plane at a distance 10cm from the wall (as

$F = ma$
$qE = ma$
$a = \dfrac{qE}{m}$
Now $d = \dfrac{1}{2}a{t}^{2}$
$t = \sqrt{\dfrac{2d}{a}}$
$t = \sqrt{\dfrac{2d}{\left(\dfrac{qE}{m}\right)}}$

$t = \sqrt{\dfrac{2 \times 0 . 1}{\left(\dfrac{8 \times {10}^{- 6}}{{10}^{- 3}}\right) \times 100}} = \dfrac{1}{2}$
$∴$ Time period $= 2t = 1s$
Answer $= 1 . 00$

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