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9th Class Science Work and energy Question Bank Work, Energy and Power

  • question_answer
    A stone of mass m kg is whirled in a vertical circle of radius 20 cm. The difference in the kinetic energies at the lowest and the topmost positions is

    A)  4 mg joules      

    B)         0.4 mg joules  

    C)  40 mg joules     

    D)         None of these

    Correct Answer: B

    Solution :

     Difference in \[K.\text{ }E.=\]Difference in\[P.E.\]                 \[=mgh=2mgr\]                                \[(\because \,\,h=2r)\]                 \[=2mg\times 0.2\]                 \[=\mathbf{0}\mathbf{.4}\,\,\mathbf{mg}\]joules


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