Which statement is true about the motion of a planet in its orbit around the Sun?

Question

Perigee is when the orbital speed is at its least.
The orbital speed of the planet remains constant as it orbits the Sun.
The orbital speed increases as the planet approaches apogee.
The planet's orbital speed changes as it moves closer and farther from the Sun.

Answer 1

The true statement about the motion of a planet in its orbit around the Sun is:

The planet's orbital speed changes as it moves closer and farther from the Sun.

This is consistent with Kepler's laws of planetary motion, specifically Kepler's second law (the law of areas), which states that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This means that a planet moves faster when it is closer to the Sun (at perihelion, which is the closest point in its orbit) and slower when it is farther from the Sun (at aphelion, which is the farthest point in its orbit).

The other statements are incorrect:

• Perigee is not relevant here, as this term typically refers to the closest point in an orbit around a planet, whereas "perihelion" refers to the closest point in an orbit around the Sun.
• The orbital speed of a planet does not remain constant; it changes as the planet moves through its elliptical orbit.
• The orbital speed increases as the planet approaches perihelion, not apogee.