The height ‘ h ’ at which the weight of a body will be the same as that at the same depth &lsquo…

The height ‘h’ at which the weight of a body will be the same as that at the same depth ‘h’ from the surface of the earth is (Radius of the earth is R and effect of the rotation of the earth is neglected) 
  1. 52R-R
  2. R2
  3. 5R-R2
  4. 3R-R2

Solution

GM(R+h)2=GMR3(R-h)
R3=(R+h)2(R-h)
=R2+h2+2hR(R-h)
R3=R3+h2R+2hR2-R2h-h3-2h2R
h3+h2(2R-R)-R2h=0
h3+h2R-R2h=0
h2+hR-R2=0
h=-R±R2+4(1)R22
=-R+5R2
=(5-1)2R

Asked in: JEE Main 2020 (02 Sep Shift 2)

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