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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        A disc of mass 10 g is kept horizontally in air by firing bullets of mass 5 g each at the rate of 10 per second. If the bullets rebound with the same speed, what is the velocity with which the bullets are fired?

    A)  49cm/s                               

    B)  98 cm/s

    C)  147 cm/s            

    D)  196 cm/s

    Correct Answer: B

    Solution :

                    Rate of change of momentum of bullet = weight of disc ie,         \[m\frac{dv}{dt}=Mg\] \[5\times {{10}^{-3}}\times 10[v-(-v)]=10\times {{10}^{-3}}\times 9.8\]                 \[5(2v)=9.8\]                 \[v=\frac{9.8}{10}m/s\]                 \[=\frac{9.8}{10}\times 100\,cm/s\]                 \[=98\text{ }cm/s\]


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