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A planet moves around the Sun on an elliptical path. At which point of the orbit is the planet's linear (orbital) speed the greatest?

1. At perihelion (closest point to the Sun)
2. At aphelion (farthest point from the Sun)
3. At the ends of the minor axis
4. The speed is the same everywhere

Correct answer: At perihelion (closest point to the Sun)

Solution

Angular momentum is conserved, so the planet sweeps equal areas in equal times. It must move fastest where it is closest to the Sun (perihelion) and slowest at aphelion.

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