Answer: 90 min.
- A 30 min
- B 90 min
- C 6 hours
- D 12 hours
Correct answer: B. 90 min
Explanation: Low Earth orbit satellites (ISS, etc.) have orbital periods of about 90 minutes.
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.