NEET Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति NEET PYQ-Work Energy Power and Collision

  • 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: [AIPMT (S) 2004]

    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\[=p\]
    \[\therefore \]      \[E=\frac{p}{2m}\] 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         \[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{{{m}_{2}}}{{{m}_{1}}}\]
    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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