Answer: −GMm/2r.
- A −GMm/r
- B −GMm/2r
- C +GMm/2r
- D −GMm/4r
Correct answer: B. −GMm/2r
Explanation: E = KE + PE = GMm/2r − GMm/r = −GMm/2r.
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.