JEE Main 2020PhysicsElectrostaticsHardMCQ

JEE Main 2020 — Electrostatics Question with Solution

JEE Main 2020 (05 Sep Shift 1)

Question

A solid sphere of radius R carries a charge Q+q distributed uniformly over its volume. A very small point like piece of it of mass m gets detached from the bottom of the sphere and falls down vertically under gravity. This piece carries charge q. If it acquires a speed ν when it has fallen through a vertical height y (see figure), then (assume the remaining portion to be spherical)

Choose an option

Show full solutionCorrect option: D
Correct answer
Dv2=2yqQ4πε0R(R+y)m+g

Step-by-step explanation

By using total energy conservation
ΔKE+(ΔPE)electo +(ΔPE)gravitation =0

12mV2+kQqR+y-kQqR+(-mgy)=0

12mV2=mgy+kQq1R-1R+y;  V2=2gy+2kQqmyR(R+y)

V2=2yqQ4πε0R(R+y)m+g

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About this question

This is a previous-year question from JEE Main 2020, covering the Electrostatics chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.