JEE Main & Advanced Physics NLM, Friction, Circular Motion JEE PYQ - NLM Friction Circular Motion

  • question_answer
    A bullet of mass 4g is fired horizontally with a speed of 300 m/s into 0.8 kg block of wood at rest on a table. If the coefficient of friction between the block and the table is 0.3, how far will the block slide approximately? [JEE ONLINE 12-04-2014]

    A) 0.19 m

    B) 0.379 m

    C) 0.569 m

    D) 0.758 m

    Correct Answer: B

    Solution :

    [b] Given, \[{{m}_{1}}=4g,{{u}_{1}}=300m/s\]
    \[{{m}_{2}}=0.8kg=800g,{{u}_{2}}=0m/s\]
    From law of conservation of momentum,
    \[{{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}={{m}_{1}}{{v}_{1}}+{{m}_{2}}{{v}_{2}}\]
    Let the velocity of combined system = v m/s
    then,\[4\times 300+800\times 0=(800+4)\times v\]
    \[v=\frac{1200}{804}=1.49m/s\]
    Now, \[\mu =0.3\] (given)
    \[a=\mu g\]
    \[a=0.3\times 10\]                      (take \[g=10\,m/{{s}^{2}}\])
    \[=3m/{{s}^{2}}\]then, from \[{{v}^{2}}={{u}^{2}}+2\]as
    \[{{(1.49)}^{2}}=0+2\times 3\times s\]\[s=\frac{{{\left( 1.49 \right)}^{2}}}{6}\]
    \[s=\frac{2.22}{6}\]
    \[=0.379m\]


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