A girl of mass 50 kg sits in a swing formed by a rope of 10 m length.A person pulls the swing to a side so that rope makes an angle of 60 with the vertical.What is the gain in potential energy of the girl?

When swing is pulled apart the vertical height of the swing h= 10 cos60°=10/2 =5m.therefore the height by which the swing is raised = l-h = 10-5 = 5m.therefore the rise in the potential energy =mgh = 50×10×5= 2500 J.

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