JEE Main & Advanced Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति JEE PYQ - Work Energy Power and Collision

  • question_answer
    A body of mass \[m={{10}^{-2}}kg\]is moving in a medium and experiences a frictional force \[m={{10}^{-2}}kg\]Its intial speed is \[{{v}_{0}}=10m{{s}^{-1}}.\]If, after 10 s, its energy is\[\frac{1}{8}mv_{0}^{2},\] [JEE Main 2017]

    A) \[{{10}^{-4}}kg\,{{m}^{-1}}\]

    B) \[{{10}^{-1}}kg\,{{m}^{-1}}{{S}^{-1}}\]

    C) \[{{10}^{-3}}kg\,{{m}^{-1}}\]           

    D) \[{{10}^{-3}}kg\,{{s}^{-1}}\]

    Correct Answer: A

    Solution :

    [a] \[\frac{1}{2}mv_{f}^{2}=\frac{1}{8}mv_{0}^{2}\]
                \[{{v}_{f}}=\frac{{{v}_{0}}}{2}=5\,m/s\]
    \[({{10}^{-2}})\frac{dv}{dt}=-k{{v}^{2}}\]
    \[\int_{10}^{5}{\frac{dv}{{{v}^{2}}}}=-1000k\int_{0}^{10}{dt}\]
    \[\frac{1}{5}-\frac{1}{10}=100\,k(10)\]
    \[k={{10}^{-4}}\]


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