Question

The work done by a man in holding a 15 kg suitcase while waiting for a bus for 45 minutes is?
(A) 675 J
(B) 405 J
(C) 450 J
(D) Zero

Answer 1

We need to find the scientific work done which is different from the mechanical work. If we look at it from the mechanical point of view, the work is done in holding the weight and that too for a long time. The scientific work done is given by the dot product of the force and the displacement. We know that both the force and the displacement are vector quantities, so we have to take into account their directions too.

Complete answer:
When the man is holding the suitcase the only force which is acting on the suitcase is the gravitational force which acts vertically downwards but there is no displacement of the suitcase. Since, the displacement is zero and work is the dot product of force and displacement, so the work done is equal to zero.

Hence, the correct option is D.

Note: Remember work is a scalar quantity and it is given as the dot product of the force acting on the body and the displacement of the body during the course of time. The two vectors can be aligned to one another at some angle.Dot product or scalar product of two vectors is given by $\overrightarrow{A}.\overrightarrow{B}=AB\cos \alpha$
Where $\alpha$is the angle between the two vectors. If either of the vector’s magnitude is zero, then the dot product of the vectors comes out to be zero.