Question

What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

Answer 1

Hint : To solve this question, we have to know about the work done also. We know that, Work done is defined in such a way that it involves both Force applied on the body and the displacement of the body.

Complete Step By Step Answer:
Work is done whenever the given two conditions are satisfied:
We know that, A force acts on the body.
There is a displacement of the body by applying force in or opposite the force’s direction.
If the direction of force is perpendicular to displacement, then the work done is zero. When a satellite moves around the Earth, then the force of gravity on the satellite is perpendicular to its displacement. Hence, the work done on the satellite by the Earth is zero.
We can also say, when a satellite revolves around the earth in circular orbit, the earth applies a gravitational force on the satellite in direction towards the center of earth but the satellite moves in tangential direction to the orbit.
Therefore force of gravity and displacement are perpendicular to each other.
Hence, the work done by force of gravity on the satellite is Zero.

Note :
We also have to know that the unit you should use for work done and energy is the joule (J) which is indeed the same as the newton meter (N m). There is another physical quantity which is the product of force and distance and that is torque or moment of a force. The unit you should use for torque is the newton meter (Nm) and not the joule.