The figure below shows a planet travelling in a clockwise direction on an elliptical path around a star located at one focus of the ellipse. When the planet is at point A:
A)its speed is constant.
B)its speed is increasing.
C)its speed is decreasing.
D)its speed is a maximum.
E)its speed is a minimum.

Question

The figure below shows a planet travelling in a clockwise direction on an elliptical path around a star located at one focus of the ellipse. When the planet is at point A: 
A)its speed is constant. 
B)its speed is increasing. 
C)its speed is decreasing. 
D)its speed is a maximum. 
E)its speed is a minimum.

Quizplus · Accepted Answer

According to Kepler's second law, a planet in orbit around a star sweeps out equal areas in equal time intervals. Therefore, when the planet is at point A, it is closer to the star, and therefore must move faster to sweep out the same amount of area as when it is farther from the star. This means that its speed is decreasing as it moves towards point A.

The Figure Below Shows a Planet Travelling in a Clockwise