Q68 / 90 · JEE Main 2024 (30 Jan Shift 1) · Physics

The gravitational potential at a point above the surface of earth is -5.12×107 J kg-1 and the acceleration due to gravity at that point is 6.4 m s-2. Assume that the mean radius of earth to be 6400 km. The height of this point above the earth's surface is:

  • Correct answer
    A
    1600 km
  • B
    540 km
  • C
    1200 km
  • D
    1000 km

Solution

Gravitational potential at a distance r from the centre of the earth is given by, V=-GMr.

Therefore, we can write

-GMERE+h=-5.12×107    …i

also acceleration due to gravity at that point will be

GMERE+h2=6.4    …ii

By (i) and (ii), we get

-GMERE+hGMERE+h2=5.12×1076.4

⇒RE+h=80×105 m=8000 km⇒h=8000 km-6400 km=1600 km

Hence, the correct answer is option: 'A'.

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