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

Options

A. Work done by all forces on man is equal to the rise in potential 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 .

Answer

B, D

Explanation

Work done by gravitational force on man = - mgL
Work done by muscular force = mgL
` :. ` W.D by all the forces on man ` = - mgL +mgL = 0 `
(air resistance neglected )
And the reaction force from a step does no work because the point of application of the force is not moving while the force exists .