Question

In each of the following a force, $F$ is acting on an object of mass $M$. The direction of displacement is from west to east shown by the longer arrow. Observe the diagram carefully and state whether the work done by the force is negative, positive, or zero.

Answer 1

Workdone $W=\overrightarrow{F}.\overrightarrow{S}=FS$ $cos\theta$ where $\theta$ is the angle between $\overrightarrow{F}$ and $\overrightarrow{S}$

For (a) : $\theta ={90}^{\circ }$

$\therefore$ $W=FS$ $cos{90}^{\circ }=0$

For (b) : $\theta =0^{\circ }$

$\therefore$ $W=FS$ $cos{0}^{\circ }=FS>0$

For (c) : $\theta ={180}^{\circ }$

$\therefore$ $W=FS$ $cos{180}^{\circ }=-FS<0$