Question

What is work done by the moon when it revolves around the earth.

Answer 1

Hint: As we know that, the work done is the product of displacement and force applied in the direction of displacement. Hence, the work done by the moon when it revolves around the earth can be calculated by considering the direction of motion of the moon and the force applied on it.

Complete solution:
We know that, when the moon revolves around the Earth, the force which is applied on the moon is the force of gravity. The force of gravity always acts centre of the earth, but the direction in which the moon is moving is always $90{}^\circ $ to the force of gravity. Hence, work done of moon in this case would be,
${{W}_{m}}=FS\cos \theta $
Where,
$F=$ Force of gravity
$S=$ direction of motion of moon or displacement.
$\cos \theta =$ angle between two vectors i.e. force and displacement
Angle $=90{}^\circ $ (in this case)
If we simplify this question by putting
$\theta =90{}^\circ $
We get,
${{W}_{m}}=FS\cos \left( 90{}^\circ \right)$
But we know that $\cos 90{}^\circ =0\left( zero \right)$
Thus we have;
$\therefore {{W}_{m}}=FS\left( 0 \right)$
$\therefore {{W}_{m}}=0\left( zero \right)$
Hence, we can say that the work done by the moon when it revolves around the earth is always $0\left( zero \right)$.

Note: The force of gravity is the force due to which the moon revolves around the earth. In the universe, the body attracts each other because of the gravitational force. According to the gravitational law any two bodies will attract each other and this force attraction will be directly proportional to the product of their masses and inversely proportional to the square of the distance between them.