question_answer

               An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object? 

Answer:

                  Force of the gravity = mg (vertically downward everywhere) Displacement of object AB (= s say) in horizontal direction. Angle between force and displacement is 90°. Work done, W = Fs cos 90°= 0 (zero) That is work done by gravity on projectile is zero.