Read the passage below and answer the question <br><br>
If the displacement of an object is perpendicular to the force acting on it, the work done by the force on the object is zero. Consider for example, the force of gravity acting on an aero plane flying
in the sky. The force of gravity is in the downward direction, whereas the aero plane's displacement is in the horizontal direction, I.e; the force and the displacement are perpendicular to each other. There is no displacement in the direction of the force of gravity, and therefore, the work done by it on the aero plane is zero.<br><br>
QUESTION : When the porter climbs up a staircase the work done is
