Why does the speed of a planet decrease as it moves away from the Sun?

Question

A. The direction of the Sun's pull relative to the planet's motion changes
B. The planet's inertia begins to point inward toward the Sun
C. The sun's gravitational pull on the sun decreases
D. The planet's inertia begins to point backward along its orbit

Answer 1

The correct answer is A. The direction of the Sun's pull relative to the planet's motion changes.

As a planet moves away from the Sun, the gravitational force exerted by the Sun does decrease slightly due to the increased distance, but the major factor affecting the planet's speed is the change in direction of the gravitational force relative to the planet's motion. According to Kepler's laws of planetary motion, planets move faster when they are closer to the Sun (at perihelion) and slower when they are further away (at aphelion). This is influenced by the gravitational pull, which always acts toward the Sun, affecting the planet's velocity as it travels along its elliptical orbit.