Question

Two planets, planet A and planet B, have the same surface gravity. However, planet B has twice the radius of planet A. How does the mass of planet B compare to the mass of planet A?

Answer 1

the surface gravity acceleration is given by

g = GM/r^2

Where M is the mass of the planet ant r is the radius of the planet

If they are the same then

GM1/r1^2 = GM2/r2^2

but you know r1=2r2 so you can work out M1/M2