A planet is moving in an elliptical orbit around the sun. If $$T, U, E$$  and $$L$$ stand for its kinetic energy, gravitational potential energy, total energy and magnitude of angular momentum about the centre of force, which of the following is correct?

Solution :
When the planet moves in circular or elliptical orbit, then torque is always acting parallel to displacement or velocity. So, angular momentum is conserved. When the field is attractive, then potential energy is given by $$U = - \frac{{GMm}}{R}$$
Negative sign shows that the potential energy is due to attractive gravitational force. Kinetic energy changes as velocity increases when distance is less. Hence, option (C) is correct.