Question

A girl is running through a circular path with a uniform speed. How much work is done by the girl ?

Answer 1

Work done = Force(F) × displacement (s)

Work done is zero in the following cases :
1.If F = 0
2.If s =0
3.If F s cos 90 degrees. (If F and s are perpendicular )



If the girl is moving around a circular path , there will be no displacement.

∴ Work done = 0


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Answer 2

The work done by girl is zero.

This can be explained by 2 ways :

1. When the girl completes one full revolution in the circular path, the net displacement of the girl is zero.

So, work done is :

$W = F \times d$

$\implies \: W = F \times 0$

$\implies \: W = 0 \: joule$

2. When the girl is moving on a circular trajectory the centripetal force vector is perpendicular to the displacement vector.

So, work done is :

$W = F \times d \times \cos( \theta)$

$\implies W = F \times d \times \cos( {90}^{ \circ} )$

$\implies W = 0 \: joule$

So, on a circular trajectory, work done is always zero.