Question:

As shown in figure, $a$ planet revolves in elliptical orbit around the sun, where $K.E.$ of the planet is maximum :

Updated On: Jul 27, 2022
  • at $P_{4}$
  • at $P_{1}$
  • at $P_{2}$
  • at $P_{3}$
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The Correct Option is A

Solution and Explanation

Since angular momentum is conserved Therefore, $I_{1} \omega_{1}=I_{2} \omega_{2}$ or $M R_{1}^{2} \omega_{1}=M R_{2}^{2} \omega_{2}$ or $M R_{1} v_{1}=M R_{2} v_{2}$ At $P_{4}$ the value of $R$ is minimum Hence the velocity is maximum or kinetic energy will be maximum.
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Concepts Used:

Keplers Laws

Kepler’s laws of planetary motion are three laws describing the motion of planets around the sun.

Kepler First law – The Law of Orbits

All the planets revolve around the sun in elliptical orbits having the sun at one of the foci.

Kepler’s Second Law – The Law of Equal Areas

It states that the radius vector drawn from the sun to the planet sweeps out equal areas in equal intervals of time.

Kepler’s Third Law – The Law of Periods

It states that the square of the time period of revolution of a planet is directly proportional to the cube of its semi-major axis.

T2 ∝ a3