Question

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

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Solution

## Work done by forceWork 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.The work done by a body is defined by the form, $w=F×ds×\mathrm{cos}\theta$, where F is the force exerted on the body and s is the displacement of the body due to the force.ExplanationThe boy carrying a bag on his shoulders walking horizontally. So, the displacement of the boy and the bag is horizontal.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.CalculationNow, from the formulae of work done, $w=F×ds×\mathrm{cos}\theta =0\phantom{\rule{0ex}{0ex}}orw=0.$, As we know $\mathrm{cos}90=0$.Therefore, the boy carrying a bag on his shoulders walking at an angle of 90 degrees, in this case, the work done is zero.

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