Answer: 6.67 x 10-11 N.
- A 6.67 x 10-11 N
- B 9.8 N
- C 1 N
- D 6.67 x 10-8 N
Correct answer: A. 6.67 x 10-11 N
Explanation: F = Gm1m2/r2 = 6.674 x 10-11 x 1 x 1 / 12 = 6.67 x 10-11 N.
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.