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 zero b) work done by all the force 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
Correct options are B) and D) Work done is defined as product of the force and the distance over which the force is applied. Work is done when a force is applied to an object and the object is moved through a distance. Distance moved by point where the force is applied is zero. Because staircase is stationary amd feet on that are also stationary. So work done by normal force acting on the feet is zero. So best possible answer is option B,D.
