Answer: 15.8 km/s.
- A 11.2 km/s
- B 15.8 km/s
- C 22.4 km/s
- D 5.6 km/s
Correct answer: B. 15.8 km/s
Explanation: v<sub>e</sub> ∝ √M for fixed R, so v = 11.2√2 ≈ 15.8 km/s.
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.