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

A man of mass m , standing at the bottom of the staircase of height L

1.	A man of mass m , standing at the bottom of the staircase of height L climbs it and stands at its top .
Answer» Work done by all forces on MAN is equal to the RISE in potentialenergy mgL . Work done by all forces on man is zero The bullet will move in a different parabolic path The reaction from a step does not do work becausethe point of application of the forces does not move while the force exists . Solution :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 CHANGEIN kinetic energy is almost zero. As the pointon whichconatct forces are applied does not move hence work done by reaction forces will be zero .