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NEET Physics NLM, Friction, Circular Motion NEET PYQ-NLM Friction Circular Motion

  • question_answer
    An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of \[12\,m{{s}^{-1}}\] and the second part of mass 2 kg moves with \[8\,m{{s}^{-1}}\] speed. If the third part flies off with \[4\,m{{s}^{-1}}\] speed, then its mass is                                               [NEET 2013]

    A) 3 kg

    B) 5 kg

    C) 7 kg

    D) 17 kg

    Correct Answer: B

    Solution :

    We have \[{{p}_{1}}+{{p}_{2}}+{{p}_{3}}=0\]          \[[\because P=mv]\]
    \[\therefore \]      \[1\times 12i+2\times 8j+{{p}_{3}}=0\]
    \[\Rightarrow \]   \[12i+16j+{{p}_{3}}=0\]
    \[\Rightarrow \]   \[{{p}_{3}}=-(12i+16j)\]
    \[\therefore \]            \[{{p}_{3}}=\sqrt{{{(12)}^{2}}+{{(16)}^{2}}}\]
    \[\sqrt{144+256}\]
    \[=20kg-m/s\]
    Now,     \[{{p}_{3}}={{m}_{3}}{{v}_{3}}\]
    \[\Rightarrow \]   \[{{m}_{3}}=\frac{{{p}_{3}}}{{{v}_{3}}}=\frac{20}{4}=5kg\]


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