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

  • question_answer
    A ball dropped from a \[20\,\,m\] height loses \[40%\] of its energy on hitting the ground. Up to what height does the ball rebound?

    A) \[28\,\,m\]        

    B)        \[8\,\,m\]

    C) \[12\,\,m\]          

    D)        \[20\,\,m\]

    Correct Answer: C

    Solution :

     Let \[{{h}_{2}}\] be the height to which ball rebounds. Given,\[%\] loss of energy \[=\frac{mg{{h}_{1}}-mg{{h}_{2}}}{mg{{h}_{1}}}\times 100\],            \[40=\frac{20-{{h}_{2}}}{20}\times 100\]


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