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9th Class Science Work and energy Question Bank Work Power and Energy IIT JEE Objective Problems

  • question_answer
    A stone is projected vertically up to reach a maximum height h. The ratio of its K.E. to P.E, at a height\[\frac{4h}{5}\]will be

    A)  5 : 4                                      

    B)  4 : 5

    C)  1 : 4                      

    D)  4 : 1

    Correct Answer: C

    Solution :

      At highest point total energy \[(T.E)=mgh\] We have to find, K.E. : P.E. at height \[\frac{4th}{5}\] For this we have to find K.E. = ? and P.E. =? We know, \[P.E.=mgh\Rightarrow m\times g\times \frac{4h}{5}=\frac{4}{5}mgh\] We also know that, \[T.E.=K.E.+P.E.\] \[\Rightarrow mgh=K.E.+\frac{4}{5}mgh=\frac{1}{5}mgh\] \[\therefore \frac{K.E.}{P.E.}=\frac{\frac{1}{5}mgh}{\frac{4}{5}mgh}=\frac{1}{4}\] Therefore, \[K.E.=1:4\]


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