A man starts walking from a point on the surface of earth (assumed smooth) and reaches diagonally opposite point. What is the work done by him
a) Zero b) Positive
c) Negative d) Nothing can be done
Since surface is smooth, no work is done against friction.
Since the person is at the same distance (equal to Radius of Earth) from the center of the earth, there is no change in potential energy and so no work is done.