A planet is moving in an elliptical orbit around the sun. If $T$, $V$, $E$ and $L$ stand respectively 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? (1990)

$T$ is conserved

$V$ is always positive

$E$ is always negative

$L$ is conserved but direction of vector $L$ changes continuously

Solution:

For a bound elliptical orbit, total energy $E$ is always negative. $T$ and $V$ vary with distance, and $L$ is conserved in both magnitude and direction as Torque is Zero. Gravitational force is passing through Center of Rotation so Toque is zero.

Rankers Physics

A planet is moving in an elliptical orbit around the sun. If $T$, $V$, $E$ and $L$ stand respectively 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? (1990)

Solution: