Answer: r 3.
- A r
- B r<sup>2</sup>
- C r<sup>3</sup>
- D r<sup>4</sup>
Correct answer: C. r<sup>3</sup>
Explanation: Kepler's third law: T<sup>2</sup> is proportional to r<sup>3</sup> (square of period proportional to cube of orbital radius).
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.