Question

Why is work done negative only when cos theta is 90<theta<= 180 but not when it is 90<theta <270 .

Answer 1

Answer

Work done by force is given by

$W=Fdcos\theta$

Work will be negative or positive it will depend upon the value of $cos\theta$

When $90°<\theta<270°$ then value of cos$\theta$ will be negative so work done will be negative.

When value of theta $0°<\theta<90° and \space 270°<\theta<360°$

Then value of cos$\theta$ will be positive.

So work done will be positive.