Answer: 6.67 x 10 -11 N.
- A 6.67 x 10<sup>-11</sup> N
- B 9.8 N
- C 1 N
- D 6.67 x 10<sup>-8</sup> N
Correct answer: A. 6.67 x 10<sup>-11</sup> N
Explanation: F = Gm<sub>1</sub>m<sub>2</sub>/r<sup>2</sup> = 6.674 x 10<sup>-11</sup> x 1 x 1 / 1<sup>2</sup> = 6.67 x 10<sup>-11</sup> 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.