Physics question

[TheBoneDoctah]

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[DrknoSDN]

(B) gravitational force is proportional to the inverse of the square of the radius. Additionally gravitational force depends on both masses. (F=GMm/r^2)
Planet A is half the radius so four times gravitational field strength at that radius, but the mass is only half as massive.
Net of double the gravitational force on the object.

also, answers are in the back of the book.