A moon is in orbit around its mother planet. Which of the following statements is always true about its kinetic energy (K), and its gravitational potential energy (U)?
A) K is positive, and U is positive.
B) K is negative, and U is negative.
C) K is positive, and U is negative.
D) K is negative, and U is positive.

Question

Quizplus · Accepted Answer

In an orbital system, the kinetic energy (K) of an object is always positive because it is defined as $ \frac{1}{2}mv^2 $, where $ m $ is the mass and $ v $ is the velocity of the object, both of which are always positive. The gravitational potential energy (U), on the other hand, is considered negative due to the convention that it is zero at an infinite distance away from the planet and decreases (becomes more negative) as the object approaches the planet.

A Moon Is in Orbit Around Its Mother Planet