Question

A boy carrying a bag on his shoulders walking at angle of 90 degrees does any work or not

Answer 1

Work done by force

1. Work done is the total amount of necessary energy to bring a body from one point to another point. Work done is the dot product of force and displacement.
2. The work done by a body is defined by the form, $w=F\times ds\times \cos \theta$, where F is the force exerted on the body and s is the displacement of the body due to the force.

Explanation

1. The boy carrying a bag on his shoulders walking horizontally. So, the displacement of the boy and the bag is horizontal.
2. But, due to the bag, a weight (gravitational force) is acting downwards (vertically). So, the displacement and applied force of the boy are perpendicular to each other, i.e, the angle between displacement and force is ${90}^o$. So, the work done is zero.

Calculation

Now, from the formulae of work done,

$$\begin{gathered} w=F\times ds\times \cos \theta =0 \\ orw=0. \end{gathered}$$,

As we know $\cos 90=0$.

Therefore, the boy carrying a bag on his shoulders walking at an angle of 90 degrees, in this case, the work done is zero.