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.

Work done by all forces on man is equal to the rise in potential energy `mgL`.

Work done by all forces on man is zero

Work done by the gravitational force on man is `mgL`

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.

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The correct Answer is:

B, D

When a man of mass `m` climbs up the staircase of height `L`, work done by the gravitation force on man is `(-)mgL`, and work done by muscular force is `mgL`. If we ignore air resistance and friction, then the work done by all forces on man is equal to `-mgL+mgL=zero. `Further , reaction force from a step does not do work because the point of application of force does not move while the force exists.

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