If a newly discovered planet has four times the mass of Earth, but it still has the same surface gravity as Earth, how big must this new planet be?
A) four times as large as Earth
B) twice as large as Earth
C) the same size as Earth
D) half the size of Earth
E) one fourth of the size of Earth

Question

Quizplus · Accepted Answer

The surface gravity of a planet is determined by its mass and radius. If the new planet has four times the mass of Earth but the same surface gravity, its radius must be larger to compensate. Specifically, the radius must be √4 = 2 times larger, meaning the planet is twice as large as Earth.

If a Newly Discovered Planet Has Four Times the Mass