A body having specific charge 8,μ {C} / {g} is resting on a frictionless plane at a distance 10, {c

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1. Electric Charges and Fields

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A body having specific charge $8\,\mu {C} / {g}$ is resting on a frictionless plane at a distance $10\, {cm}$ from the wall (as shown in the figure). It starts moving towards the wall when a uniform electric field of $100 \,{V} / {m}$ is applied horizontally toward 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

$1$

B

$5$

C

$7$

D

$8$

(JEE MAIN-2021)

Solution

$F=m a$

$q E=m a$

$a=\frac{q E}{m}$

Now $d=\frac{1}{2} a t^{2}$

$t=\sqrt{\frac{2 d}{a}}$

$t=\sqrt{\frac{2 d}{\left(\frac{q E}{m}\right)}}$

$t=\frac{2 \times 0.1}{\left(\frac{8 \times 10^{-6}}{m 10^{-3}}\right) \times 100}=\frac{1}{2}$

Standard 12

Physics

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