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When is the work done on the body said to be zero ?

Answer» <html><body><p></p>Solution :The work done on the body be zero under following situationusingformula `W = fd <a href="https://interviewquestions.tuteehub.com/tag/cos-935872" style="font-weight:bold;" target="_blank" title="Click to know more about COS">COS</a> theta `<br/> (1) Work done is zerowhenthe force.Asfor example, a blockmovingon a smoothhorizontaltableis notactedupon by a horizontalforcebutmayundergoa largedisplacement . <br/> (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 .<br/> (<a href="https://interviewquestions.tuteehub.com/tag/3-301577" style="font-weight:bold;" target="_blank" title="Click to know more about 3">3</a>) When force and displacement are mutually perpendicular . <br/> <img src="https://doubtnut-static.s.llnwi.net/static/physics_images/KPK_AIO_PHY_XI_P1_C06_E01_015_S01.png" width="80%"/><br/> 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 . <br/> (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 . <br/> For example: A <a href="https://interviewquestions.tuteehub.com/tag/cylinder-942617" style="font-weight:bold;" target="_blank" title="Click to know more about CYLINDER">CYLINDER</a> 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 .<br/> <img src="https://doubtnut-static.s.llnwi.net/static/physics_images/KPK_AIO_PHY_XI_P1_C06_E01_015_S02.png" width="80%"/><br/> (b) A sphere is placed in a V - shaped ditch as shown in figure (<a href="https://interviewquestions.tuteehub.com/tag/c-7168" style="font-weight:bold;" target="_blank" title="Click to know more about C">C</a> ). There are three forcesacting on it . Even though it doesn.t <a href="https://interviewquestions.tuteehub.com/tag/move-548879" style="font-weight:bold;" target="_blank" title="Click to know more about MOVE">MOVE</a> . So the displacement by every force is zero and hence total work is also zero .</body></html>


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