Suppose a planet has an elliptical orbit.The speed of the planet is 20 km/s when it is at its average distance from the Sun.Which of the following is most likely to be the planet's speed when it is farthest from the Sun?
A)15 km/s
B)20 km/s
C)25 km/s
D)30 km/s

Question

Quizplus · Accepted Answer

According to Kepler's laws of planetary motion, a planet moves faster when it is closer to the Sun and slower when it is farther away. Therefore, when the planet is at its farthest point from the Sun (which is also called the aphelion), it will be moving at a slower speed than its average speed. Since the planet's average speed is given as 20 km/s, it is most likely that its speed when it is farthest from the Sun will be less than 20 km/s. Among the given choices, the only option that is less than 20 km/s is 15 km/s. Therefore, the best choice is A)15 km/s.

Suppose a Planet Has an Elliptical Orbit