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It is known to us that a planet revolves around the sun in an elliptical orbit with the sun at one of the foci. If the point in the orbit nearest to the sun is called the perihelion and the point farthest from the sun is called the aphelion, which of the following statement is correct? 

It is known to us that a planet revolves around the sun in an elliptical orbit with the sun at one of the foci. If the point in the orbit nearest to the sun is called the perihelion and the point farthest from the sun is called the aphelion, which of the following statement is correct?  Correct Answer The kinetic energy of the planet is minimum when it is at aphelion.

The correct answer is option 2) i.e. The kinetic energy of the planet is minimum when it is at aphelion.

CONCEPT:

  • Kepler's first law of planetary motion:
    • It states that all the planets revolve around the sun in elliptical orbits having the sun at one of the foci.
    • This law is also known as the Law of Orbits.
    • Aphelion is the point on the Earth's elliptical orbit that is farthest away from the Sun.
    • Perihelion is the point on the Earth's elliptical orbit that is nearest to the Sun.
    • An elliptical orbit of a planet is shown in the figure.

​EXPLANATION:

  • From the second law of Kepler's planetary motion, it is inferred that the area swept by the planet orbiting around the Sun is equal in equal durations of time.
  • As seen from the figure, the distance moved by the planet in its orbit is lesser when it is farther away from the Sun i.e. at aphelion.
  • So, the planet moves a lesser distance in the same amount of time. Hence, it is moving slower i.e. it has low speed at aphelion.
  • Kinetic energy is directly dependent on the velocity of an object.
  • Therefore, the kinetic energy of the planet is minimum when it is at an aphelion.

Related Questions

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