Answer: Simple harmonic motion.
- A Uniform acceleration
- B Free fall at g throughout
- C Simple harmonic motion
- D Uniform velocity
Correct answer: C. Simple harmonic motion
Explanation: Inside Earth, g decreases linearly with depth (g' = g(1-d/R) = g x r/R). This gives restoring force F = -kr, which is SHM.
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.