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Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class11  >>  Work, Power and Energy
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How much work is done against gravity in lifting a 3kg object through a distance of 40cm?

$\begin{array}{1 1}11.8J\\12.8J\\10.8J\\13.8J\end{array} $

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Answer : 11.8J
To lift a 3kg object at constant speed,an upward force equal in magnitude to its weight,$mg=(3)(9.8N)$,must be exerted on the object.
The work done by this force is what we refer to as the work done against gravity :
Work against gravity = $mgh$
$\qquad\qquad\qquad\quad=[(3)(9.8)N](0.40m)$
$\qquad\qquad\qquad\quad=11.8J$
answered Aug 28, 2014 by sreemathi.v
 

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