Question

A satellite is revolving round the earth in an elliptical orbit.

• A. Gravitational force on satellite may be greater than centripital force
• B. Work done by gravitational force for some small duration may be negative
• C. Power of gravitational force may be zero at an instant
• D. Power of gravitational force is always zero.

Answer 1

Answer: (A), (B), (C)

The correct options are
A Gravitational force on satellite may be greater than centripital force
B Work done by gravitational force for some small duration may be negative
C Power of gravitational force may be zero at an instant

The gravitaional force and centripetal force are not always equal when a planet is going in an elliptical orbit. Gravitational force can provide both centripetal and tangential force, so it can be greater than centripetal force. The speed of the planet is increasing and decreasing as it is revolving. This means, gravitational force is doing positive work sometimes and negative work some other time and hence, power is not always zero. Further, when the velocity of the planet is perpendicular to the gravitational force, the power delivered by the force is zero.