A 90 kg body placed at 2 R distance from surface of earth experiences gravitational pull of :
(R= Radius of earth, g=10 m s⁻²)

Solution

Physics sir · 3 steps

2R above the surface means 3R from the centre, so gravity drops by a factor of 9.

1. Measure from centre. Newton's law uses the distance from the centre of the earth, not from the surface. The body is R + 2R = 3R from the centre.

   g' = g(R/(R+h))² = g(R/3R)² = g/9

2. Find the pull. On the surface the pull is mg = 90 × 10 = 900 N. At 3R it is 900/9 = 100 N.
3. So. The body experiences a gravitational pull of 100 N, which is option (c).

The idea to keep. Gravity falls as 1/r², where r is measured from the centre. Always add R to the height above the surface before you square.

Answer from the NTA final answer key. Solution by PrepWiser.