JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2007

  • 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)  \[lo{{g}_{e}}x\]

    Correct Answer: A

    Solution :

                    From given information\[a=-kx\]where a is acceleration,\[x\]is displacement, and k is a proportionality constant. \[\frac{v\,dv}{dx}=-kx\] \[\Rightarrow \]               \[v\text{ }dv=-k\text{ }x\text{ }dx\] 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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