A man, of mass m, standing at the bottom of the staircase, of hei… - Vidyadip

MCQ

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 potential energy $\text{mgL.}$
B
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.
C
Work done by the gravitational force on man is $\text{mgL}$
✓
Both $B$ and $C$

✓

Answer

Correct option: D.

Both $B$ and $C$

Work done by gravitational force on man is $\text{(-mgL)}$ as gravitational force is downward and displacement $L$ is upward. The Work done by man to lift him up by muscular force will be $\text{(+mgL)}$ as force applied by muscles is in the direction of displacement. So net work done $\text{= -mgL + mgL = 0.}$

As there is no displacement point where the reaction acts so, Work Done by reaction torce is zero. As the velocity of person atmost zero at top. So $KE = 0.$ Hence, Work Done by reaction force is zero.

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