question_answer

How much work is done by a coolie walking on a horizontal platform with a load on his head?

Answer:

                Zero. In order to balance the load on his head, the coolie applies a force on it in the upward direction equal to its weight. His displacement is along the horizontal direction. Thus the angle between force \[\vec{F}\] and displacement \[\vec{s}\] is \[\text{9}0{}^\circ \]. Therefore work done, \[W=Fs\cos \theta =Fs\cos {{90}^{\circ }}=0.\]