Answer: -K.
- A -K/2
- B -K
- C K
- D 2K
Correct answer: B. -K
Explanation: For circular orbit: KE = GMm/(2r) = K. PE = -GMm/r = -2K. Total = KE + PE = K - 2K = -K.
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.