Manipal Medical Manipal Medical Solved Paper-2007

  • question_answer
    A particle of mass\[{{m}_{1}}\]is moving with a velocity\[{{v}_{1}}\] and another particle of mass\[{{m}_{2}}\]is moving with a velocity\[{{v}_{2}}\]. Both of them have the same momentum but their different kinetic energies are\[{{E}_{1}}\]and\[{{E}_{2}}\]respectively. If\[{{m}_{1}}>{{m}_{2}},\]then

    A)  \[{{E}_{1}}<{{E}_{2}}\]

    B)  \[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{{{m}_{1}}}{{{m}_{2}}}\]

    C)  \[{{E}_{1}}>{{E}_{2}}\]

    D)  \[{{E}_{1}}={{E}_{2}}\]

    Correct Answer: A

    Solution :

     Kinetic energy is given by \[E=\frac{1}{2}m{{v}^{2}}=\frac{1}{2m}{{(mv)}^{2}}\] but\[mv=\]momentum of the particle\[=p\] \[\therefore \] \[E=\frac{{{p}^{2}}}{2m}\] or \[p=\sqrt{2mE}\] Therefore,   \[\frac{{{p}_{1}}}{{{p}_{2}}}=\sqrt{\frac{{{m}_{1}}{{E}_{1}}}{{{m}_{2}}{{E}_{2}}}}\] but it is given that, \[{{p}_{1}}={{p}_{2}}\] \[\therefore \] \[{{m}_{1}}{{E}_{1}}={{m}_{2}}{{E}_{2}}\] Or \[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{{{m}_{2}}}{{{m}_{1}}}\] ?(i) Now\[{{m}_{1}}>{{m}_{2}}\] Or \[\frac{{{m}_{1}}}{{{m}_{2}}}>1\] ?(ii) Thus, Eqs. (i) and (ii) give \[\frac{{{E}_{1}}}{{{E}_{2}}}>1\] Or \[{{E}_{1}}<{{E}_{2}}\]


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