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  5. Work and energy

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

  • question_answer
    When a body is whirled in a circle, then work done on it is

    A)  positive

    B)  negative

    C)  zero  

    D)  infinite

    Correct Answer: C

    Solution :

     Fraction of energy lost,\[\frac{\Delta u}{u}\]                 \[=\frac{mg(h-h')}{mgh}=\frac{h-h'}{h}\] Here, \[h=2\,\,m\]and\[h'=1.5\,\,m\] \[\therefore \]  \[\frac{\Delta u}{u}=\frac{2-1.5}{2}=\frac{\mathbf{1}}{\mathbf{4}}\]


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