1

Question

Look at the activity listed here. Reason out whether or not work is done in the light of your understanding of the term 'work'.

Suma is swimming in a pond.

Open in App

Solution

**Work done**

- Work done is defined as the force applied to displace a body from its original state.
- Force and displacement are vector quantities.
- We know that the dot product of two vectors gives a scalar quantity as its result.
- Thus, work done is a scalar quantity.

If $\overrightarrow{F}$ is the force applied and $\overrightarrow{S}$ is the displacement of the body, then the work done $W$ can be given as,

$W=\overrightarrow{F}.\overrightarrow{S}$

$=FS\mathrm{cos}\theta $, where, $\theta $ is the angle between the direction of the force vector and displacement vector.

**Finding whether work is done or not**

- In order to swim a force needs to be applied by the hand inside the water, to push the water backward.
- This causes the water to exert a reaction force on Suma and she can move forward.

$\therefore \theta =180\xb0$

$=FS\mathrm{cos}180\xb0=-FS$

**Hence, the work done is negative.**

2

View More

Join BYJU'S Learning Program

Join BYJU'S Learning Program