Question

which statement is true about the motion of a planet in its orbit around the sun? (1 point)
the planets orbital speed changes as it moves closer and farther from the sun.
the orbital speed increases as the planet approaches apogee.
perigee is when the orbital speed is at its least.
the orbital speed of the planet remains constant as it orbits the sun.

Explanation:

According to Kepler's second law (the law of areas), a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This implies that when a planet is closer to the Sun (perihelion - similar concept to perigee for Earth - Moon system but for Sun - planet, here we assume the context is about Sun - planet), it moves faster (higher orbital speed) and when it is farther from the Sun (aphelion - similar to apogee conceptually for Sun - planet), it moves slower. So the orbital speed changes.

• For the option “The orbital speed increases as the planet approaches apogee”: Apogee (aphelion for Sun - planet) is the farthest point, and speed is minimum there, so this is wrong.
• For “Perigee is when the orbital speed is at its least”: Perigee (perihelion) is the closest point, speed is maximum there, so wrong.
• For “The orbital speed of the planet remains constant as it orbits the Sun”: Contradicts Kepler's second law.

Answer:

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