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WB JEE Medical WB JEE Medical Solved Paper-2008

  • question_answer
    A bullet emerge from a barrel of length 1.2 m with a speed of \[640\,\text{m}{{\text{s}}^{-1}}.\]Assuming constant acceleration, the approximate time that it spends in the barrel after the gun is fired is

    A)  4 ms                                     

    B)  40 ms

    C)  400 us                 

    D)  1s

    Correct Answer: A

    Solution :

                     Given      that,      s =1.2      m and \[v=640\,m{{s}^{-1}}\,a=?;\,u=\,0;t=?\] We have the third equation of motion \[2as={{v}^{2}}-{{u}^{2}}\] \[2a\times 1.2=640\times 640\]                 or            \[a=\frac{8\times 64\times {{10}^{3}}}{3}\]and by first equation of motion\[v=u+at\]or \[t=\frac{v}{a}=\frac{15}{4}\times {{10}^{-3}}=3.75\times {{10}^{-3}}s\approx \,4\,ms.\]


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