Two planets are orbiting a star. Planet A is closer to the star than Planet B. Which description explains the expected motion of Planets A and B?

Planet B orbits faster than Planet A.
Planet B has a shorter orbital period than Planet A.
Planet A orbits faster than Planet B.
Planet A has an equal orbital period to Planet B.

Respuesta :

Answer: Planet A orbits faster than Planet B.

Explanation:

Kepler's laws define the motion of a planet around a star. Planets move in an elliptical orbit around the star with star at one of its foci. The speeds are governed by second law of planetary motion. The line joining planet to star sweeps equal areas in equal time intervals. This means, in order to conserve angular momentum, the planet closer to sun would orbit faster than farther planets.

It is given that planet A is closer to star than planet B. This means that planet A would orbit the star faster than B.