Planets A and B orbit the same star. Planet B is four times further from the star than planet A and has twice the mass of planet A. The gravitational force of the star on planet B is ____ the force on planet A.

Answer 1

The force is proportional to M/R^2

F(B)/F(A) = M(B)/M(A) * [R(A)/R(B)]^2
= 2*(1/4)^2 = 1/8