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When is the work done on the body said to be zero ? |
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Answer» Solution :The work done on the body be zero under following situationusingformula `W = fd COS theta ` (1) Work done is zerowhenthe force.Asfor example, a blockmovingon a smoothhorizontaltableis notactedupon by a horizontalforcebutmayundergoa largedisplacement . (2) There is no displacement of bodyeven the force is exerted on it . As for example, when one push hard againsta rigidbrick wall , the force exert on the wall does not work . (3) When force and displacement are mutually perpendicular .  For example, during uniform circularmotion , the displacementof the body is always along tangent of the circle andthe force actingon the bodyis alwaystowardsthe centreof circleso forceand displacement is perpendicularto eachother . In this situation work doneby centripetal force is zero . (4) (a) When more than one force acts on body and the net force of all these forces is zero then work done is zero . For example: A CYLINDER is vertically tugwith string as shown in figure . Gravitational force of earth acting on the cylinder and hence tension in teh stringacting in upward directionbut here displacement of cylinder is zero so work done is also zero .  (b) A sphere is placed in a V - shaped ditch as shown in figure (C ). There are three forcesacting on it . Even though it doesn.t MOVE . So the displacement by every force is zero and hence total work is also zero . |
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