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Question: Answered & Verified by Expert
In older times, people used to think that the Earth was flat. Imagine that the Earth is indeed not a sphere of radius R, but an infinite plate of thickness H. What value of H is needed to allow the same gravitational acceleration to be experienced as on the surface of the actual Earth? (Assume that the Earth's density is uniform and equal in the two models).
PhysicsGravitationJEE Main
Options:
  • A 2R3
  • B 4R3
  • C 8R3
  • D R3
Solution:
1863 Upvotes Verified Answer
The correct answer is: 2R3


Applying Gauss law

E.ds=4πGmin

Where E is gravitational field at ds

Computing over colsed surface given

E2s=4πG(ρsh)

E= 4πG ρh 2 ... (1)

On the surface of earth with radius R E= G( ρ 4 3 π R 3 ) R 2

=Gρ 4 3 πR ... (2)

Equating (1) and (2)

4π Gρh 2 =Gρ 4 3 πR

h= 2R 3

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