Question

When acted upon by a force $F$, a body suffers a displacement $S$. The work done will be negative if the angle between $F$ and $S$ be:

• A. an acute angle
• B. an obtuse angle
• C. always equal to $0^0$
• D. always equal to ${90}^0$

Answer 1

Answer: (B)

an obtuse angle

If $\theta$ be the angle between force $F$ and displacement $S$, work done, $W=F.S.cos\theta$
So, work done to be negative, $cos\theta$ should be negative.
And, $cos\theta$ is negative when $\theta$ is an obtuse angle.