Ask a Doubt
Request a call back

Join NOW to get access to exclusive study material for best results

JEE Class main Answered

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, 20:07: PM
answered-by-expert 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

Application Videos

Concept Videos

Multiple Choice Questions Practice Test
Answered Unanswered My Questions My Answers
JEE main - Physics
a marble block of mass 2 kg lying on ice when a given velocity of 6 ms–1 is stopped by friction in 10 seconds then co efficient of friction is
Asked by sumalathamadarapu9 | 23 Oct, 2024, 22:06: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
show that the frequency of oscillations remain unchanged whether a mass attached to a spring is made to oscillate in the vertical or in the horizontal direction
Asked by py309649 | 13 Oct, 2024, 13:39: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
Square of the time period of revolution of a planet is proportional to the cube of the mean distance between sun and planet. If mean distance is increased by 2% then percentage change in its time period is
Asked by coolskrish | 13 Oct, 2024, 12:50: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
two particles of mass m and 4m are initially actress the sad moving towards each other due to mutual gravitational force at an instantly of m is vî then at this instant the velocity of mass 4m is
Asked by midnightmoon3355 | 09 Oct, 2024, 09:09: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
what is the second law of thermodynamics
Asked by rambabunaidu4455 | 03 Oct, 2024, 16:03: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
what is the relation between drift velocity and mobility
Asked by ratchanavalli07 | 17 Sep, 2024, 07:46: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
A ball of mass m approaches a moving wall of infinite mass with speed v along the normal to the wall. The speed of the ball is u towards the ball. The speed of the ball after elastic collision with the wall is
Asked by yayashvadutta45 | 15 Sep, 2024, 19:47: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
a current of 2a is flowing through a conductor of length 22m bent in arc radius 5cm
Asked by adithireddy999 | 03 Sep, 2024, 09:35: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
two vectors vector a and vector B lie in one plane vector c lie in the different plane then vector a + vector b + vector c is
Asked by vaishalinirmal739 | 29 Aug, 2024, 18:07: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
JEE main - Physics
What is impulse?
Asked by vradhysyam | 26 Aug, 2024, 17:17: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
My Class Videos Tests ₹ Plans Ask a Doubt