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  A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.                 

Answer:

                  The force of gravity acting on the object of mass 10 kg is in the downward direction, whereas the displacement (AB) of the object is in the horizontal direction. In this situation, the force and the displacement are perpendicular to each other. Work done, W = Fs                            = (mg) s cos 90° = 0 Therefore, the work done on the object by the gravitational force is zero.