A man climbs up from ground to first floor using a ladder/stair. Assume that his kinetic energy does not change appreciably. Predict the sign of work done by ladder (if any).
I think the answer should be 'positive' because the negative work done by gravity has to be countered and hence some external agent must do positive work on us.
But, there's a second thought. Since at each instant normal reaction is perpendicular to direction of motion (in case of stairs) (motion being lifting of leg) therefore the work done must be zero. But then a question arises - who countered gravity?
I'm confused between the two. Both sound promising but not perfect.