Question

Work is always done on a body when :

• A. a force acts on it
• B. it moves through a certain distance
• C. it experiences an increase in energy through a mechanical influence
• D. none of these

Answer 1

Answer: (C)

it experiences an increase in energy through a mechanical influence

(i) Since work $W=\overrightarrow{F}.\overrightarrow{s}=Fs\cos \theta$
If $\theta ={90}^{\circ }\Rightarrow W=0$, but force is acting on it so option (a) is not correct.

(ii) A person carrying a suit case vertically in his hand walks in a horizontal direction, no work is done, because the angle between the direction of force applied by hand on weight & direction of displacement is ${90}^{\circ }$. So option (b) is also not correct.

(iii) According to work energy theorem
work done on body $=$change in kinetic energy of the body