The gravitational force of a star on orbiting planet 1 is f1. planet 2, which is twice as massive as planet 1 and orbits at twice the distance from the star, experiences gravitational force f2. part a what is the ratio f1f2?

The answer to this question would be: F1/F2=2

Gravitational force is directly related to the mass of the object but inversely related to the quadratic of the distance to the object. In this case, the planet2 has twice the mass and twice the distance. Then, the ratio of the gravitational force compared to planet1 should be:

F1/F2

(GMm/r^2) / (GM*2m/2r^2)

(m/r^2) / (2m/4r^2)

1 / (1/2) = 2