Question

A coolie lifts an object of mass 20kg from the earth to 1.5 m and keep it on his head . Calculate the amount of work done by him

Answer 1

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$\underline{\underline{\huge{\textbf{Solution:}}}}$

Given,
Mass of the object coolie lifted $m = 20\: kg$

Object lifted to height $s = 1.5\: m$

Work done by coolie = ?

$\underline{\large{\textbf{Step-1}}}$:
Find the Force applied by the coolie to lift the object

We have,
$Force = mass \times acceleration$

$F = m\times a$

Here,
a = acceleration due to gravity (g) = $9.8\: m/s^{2}$

Substituting Values

$\implies F = 20 \times 9.8$

$\implies F = 2 \times 98$

$\implies F = 196\: kg-m/s^{2} = 196\: N$

(Since, $1\: N = 1\: kg-m/s^{2}$)

Force applied by coolie to lift the object = 196 N

$\underline{\large{\textbf{Step-2}}}$:
Find the work done by the coolie in lifting the object

We have,
$Work\: done = Force \times displacement$

$W = F \times s$

Substituting Values

$W = 196 \times 1.5$

$\implies W = 196 \times \frac{3}{2}$

$\implies W = 98 \times 3$

$\implies W = 294\: kg-m^{2}/s^{2} = 294\: J$

(Since, $1\: J = 1\: kg-m^{2}/s^{2}$)

Therefore,
Work done by coolie in lifting the object = 294 J

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