Consider two planets of mass m and 2m, orbiting the same star in circular orbits. THe more massive planet is 8.6 times as far from the star as the less massive one.
What is the ratio F1:F2 of the gravitational forces exerted on the star by the two planets?
What is the radio v1:v2 of the speeds of the two planets?
What is the radio T1:T2 of the orbital periods of the two planets?