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A man of mass m , standing at the bottom...

A man of mass `m` , standing at the bottom of the staircase of height `L` climbs it and stands at its top .

A

Work done by all forces on man is equal to the rise in potentail energy mgL

B

Work done by all forces on man is zero

C

Work done by the gravitational force on man is mgL

D

The reaction force from a step does not do work because the point of application of the force does not move while the force exists

Text Solution

Verified by Experts

(b,d) When a man of mass m climbs up the staircase of height L, work done by the gravitational force on the man is mgl work done by internal muscular forces will be mgL as the change in kinetic energy is almost zero. Hence, total work done =-mgL+mgL=0
As the point of application of the contact forces does not move hence work done by reasction forces will be zero.
NOTE: Here work done by friction will also be zero as there is no dissipation or rubbing is involved.
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