JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    A particle moves in a straight line with retardation proportional to its displacement. Its loss of kinetic energy for any displacement \[x\] is proportional to

    A) \[{{x}^{2}}\]                                      

    B) \[{{e}^{x}}\]

    C) \[x\]                                     

    D)  \[{{\log }_{e}}x\]

    Correct Answer: A

    Solution :

    From given information\[a=-kx\], where \[a\] is acceleration, \[x\] is displacement and \[k\] is a proportionality constant.                 \[\frac{v\,\,dv}{dx}=-k\,\,x\] \[\Rightarrow \]               \[v\,\,dv=-k\,\,x\,\,dx\] Let for any displacement from \[0\] to \[x\], the velocity changes from\[{{v}_{0}}\]to\[v\] \[\Rightarrow \]               \[\int_{{{v}_{0}}}^{v}{vdv=}-\int_{0}^{x}{k\,\,x\,\,}dx\] \[\Rightarrow \]               \[\frac{{{v}^{2}}-v_{0}^{2}}{2}=-\frac{k\,\,{{x}^{2}}}{2}\] \[\Rightarrow \]               \[m\left( \frac{{{v}^{2}}-v_{0}^{2}}{2} \right)=-\frac{mk\,\,{{x}^{2}}}{2}\] \[\Rightarrow \]               \[\Delta K\propto {{x}^{2}}\]      \[[\Delta K\]is loss in\[KE]\]


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