Question

Choose the correct relation of work done where angle between force (F) and displacement(s) is $\theta$.

• A. Work done is zero
• B. Negative work done
• C. Positive work done

Answer 1

Work done is expressed as W = F $\times$ S $\times$ cos $\theta$, where F is the force applied, S is the displacement of the object and $\theta$ is the angle between force and displacement. Depending upon the value of $\theta$ work may be zero, positive or negative.
Case I When $\theta ={90}^0$, the value of $cos\theta =0$. So work done is $0$
Case II When $\theta <{90}^0$, the angle is an acute angle, $cos\theta$ is positive for acute angle. So work done will be positive.
Case III When $\theta$ is greater than 90°, the angle is an obtuse angle $\cos \theta$ is negative for obtuse angle. So work done will be negative.