Answer: 1:8.
- A 1:8
- B 1:4
- C 1:2
- D 2:1
Correct answer: A. 1:8
Explanation: g = GM/R<sup>2.</sup> g<sub>A</sub>/g<sub>B</sub> = (2M<sub>B</sub>)/(4R<sub>B</sub>)<sup>2</sup> x (R<sub>B</sub>)<sup>2</sup>/M<sub>B</sub> = 2/16 = 1/8.
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.