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# Which of the following quantities remain constant in a planetary motion (Consider elliptical orbits) as seen from the sun.

A. Speed

B. Angular Speed

C. Kinetic Energy

D. Angular Momentum

Answer :

The speed of the object depends on its distance. Hence, (a) is false. The angular velocity also depends on the distance of the planets from the sun. As these distances change in an elliptical orbit, (b) is untrue. The kinetic energy depends on the speed as well. So (c) is false. The angular momentum is a conserved quantity as there’s no external torque on the system. So (D) is correct.

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