Answer: always negative.
- A always positive
- B always negative
- C always zero
- D positive at infinity
Correct answer: B. always negative
Explanation: U = -GMm/r is negative because gravity is attractive; the energy is defined as zero at infinite separation.
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.