Question

A boy pulls a uniform chain of mass M and length L hanging vertically downwards from a roof top.
The work done by him is
a) 1/2MgL
b)mgL
c)1/2 MgL
d)MgL^2​

Answer 1

Answer:

work done =force *distance moved in direction of force.

so work done =mgl

Answer 2

ANSWER:

The work done by the boy to pull the chain is mgL.

EXPLANATION:

   According to "work energy theorem", the work done to change the state of motion of any body is equal to the force or energy exerted by the body. Here the "chain hanging vertically" downward from a roof top exhibits gravitational potential energy. So to pull the chain upward the amount of work done by the boy should be equal to the potential energy experienced by the chain.

Thus,  

Work done by the boy = Potential energy experienced by the chain

Work done by the boy = mass of the chain*acceleration due to gravity*height of displacement

Let us consider, M as the mass of the chain, "acceleration due to gravity" as g and height of displacement will be L.

Thus,  

Work done by the boy = m*g*L=mgL

Thus the "work done" by the boy to pull the chain is mgL.