Question

Moon is moving in an elliptical orbit around the earth. The mass of the Moon is assumed very small compared to the mass to the earth

• A. Angular momentum of moon about the centre of the earth remains constant.
• B. The kinetic energy of moon remains constant with respect to time
• C. The linear momentum of moon remains constant in magnitude
• D. work done by gravitational force in half round must be zero

Answer 1

The correct option is A Angular momentum of moon about the centre of the earth remains constant.

Torque is zero about center hence angular momentum remains constant.
Since orbit is eleptical, linear velociy and thus linear momentum and kinetic energy will change with time. Areal velocity and not linear velocity is constant , so work done will in half cycle will not be zero.