• # question_answer 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

As force acting on planet is central in nature so torque acting on planet is zero about the satellite & hence its angular momentum remains constant. In elliptical orbit as planet revolves around the sun, the seperation between sun & planet changes & hence moment of inertia which in turn changes the angular velocity to keep angular momentum constant. $K=\frac{{{L}^{2}}}{2I}$as I changes, K also changes.