Question

A planet is revolving around the sun in an elliptical orbit. Which of the following remains constant?
a.Linear momentum.
B.Angular momentum.
C.Kinetic energy
D.Potential energy.

Answer 1

Option (b) is correct. A planet revolving in an elliptical path has a constant angular momentum.This can be justified by Kepler's Laws.According to law of equal areas, if a straight line is drawn from the centre of the sun to the centre of the planet moving on the elliptical path, it will cover equal areas in equal intervals of time. Angular momentum , L=m*r^2*w where m,r and w are the the mass, distance between the centre of the sun and the centre of the planet and angular velocity of the planet.Since, mass remains constant, angular momentum depends only on r and w.On an eliptical path, when distance increases, angular velocity reduces and when distance decreases, angular velocity increases.This is how angular momentum remains constant