Answer: 8T.
- A 2T
- B 4T
- C 8T
- D 16T
Correct answer: C. 8T
Explanation: By Kepler's third law T ∝ r<sup>3/2</sup>, so 4<sup>3/2</sup> = 8; new period = 8T.
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.