A small probe of mass m interacts gravitationally with a planet in three separate situations.
• Situation I: planet mass M, center-to-center separation 2R
• Situation II: planet mass 2M, center-to-center separation 3R
• Situation III: planet mass 0.5M, center-to-center separation R
Rank the magnitudes of the gravitational forces exerted on the probe in the three situations.
a) II > I > III
b) III > I > II
c) I > III > II
d) III > II > I