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⚛️ Physics  ·  Gravitation  ·  NEET & JEE

Planet A has twice the mass and four times the radius of planet B. Ratio of gA to gB:

Answer: 1:8.

  • A 1:8
  • B 1:4
  • C 1:2
  • D 2:1

Correct answer: A. 1:8

Explanation: g = GM/R2. gA/gB = (2MB)/(4RB)2 x (RB)2/MB = 2/16 = 1/8.

Variation of g with Height and Depthgg_surfaceAbove surface: g ∝ 1/r² (falls off curving down)Below surface: g ∝ r (falls off LINEARLY)Earth's surface (r = R)centre (r=0): g=0g is MAXIMUM exactly at the surface - it decreases in both directions, but by different laws

g is maximum at Earth's surface; going up, it falls off as 1/r² (inverse-square); going down, it falls off linearly with depth (since only the mass enclosed within radius r contributes), reaching zero at the centre.

Concept context

Universal gravitation, orbital mechanics, gravitational potential, and escape velocity.

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