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

  • question_answer
    A \[20\,\,kg\] ball is thrown upwards with a speed of\[6\,\,m\,\,{{s}^{-1}}\]. Find the maximum height it reaches\[(g=9.8\,\,m\,\,{{s}^{-2}})\].

    A) \[2.86\,\,m\]      

    B)        \[1.88\,\,m\]

    C) \[3.82\,\,m\]      

    D)        \[1.84\,\,m\]  

    Correct Answer: D

    Solution :

    \[K.E.=\frac{1}{2}m{{v}^{2}}\] \[=\frac{1}{2}(20){{(6)}^{2}}=\frac{1}{2}\times 20\times 36\,\,J=360\,\,J\] At the highest point, the kinetic energy becomes zero, thus the entire \[K.E.\] of \[360\,\,J\] is converted into\[P.E\]. So the \[P.E.\] at the highest point is\[360\,\,J\].             \[P.E.=360=20\times 9.8\times h\]             \[h=\frac{360}{20\times 9.8}=1.84\,\,m\]             \[h=\frac{360}{20\times 9.8}=1.84\,\,m\]


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