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Why in book Work done by coolie walking on level road with load on head is given zero?but when coolie starts from rest and after some time his velocity will v .so the kinetic energy of block is increased then according to work energy theorem if kinetic energy change then work must be done.so here which force is doing work on block
Asked by ashutosharnold1998 | 23 Sep, 2019, 08:07: PM
Expert Answer
In Physics, Workdone on an object is energy spent to do work on object against a force.
If work is performed on an object against a force, energy used to do work is stored in the form of potential energy.
workdone = ( force ) × (distance moved in the direction of force )
If the coolie, keeping load on his head, is moving either vertically with respect to ground or in a direction
that makes some angle θ >0 with horizontal direction, then work is performed by coolie against gravitational force
and the spent work is stored as potential energy on the load object.
If the coolie , keeping load on his head, is moving through horizontal direction,
direction of gravitationa force is perpendicular to him. Hence no workdone against gravitational force.
When coolie is carrying load on his head, gravitational force acting on his head and pressing his head
to make some displacement say -Δy of contact part of his head. To nullify this effect, coolie's muscle force
on his head dispalce his contact part of his body through same magnitude of Δy.
This is the internal workdone done by coolie's body and this workdone is stored in his muscle of head only
but not on carrying load.
If he is walking fast, again coolie's muscle force in his leg is doing some work to raise his leg against gravitational force .
Hence by Work-energy theorem, workdone performed by using his muscle force to lift his leg equals
the difference of kinetic energy. This workdone also not stored in carrying load as potential energy.
Answered by Thiyagarajan K | 24 Sep, 2019, 11:08: AM
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