JEE Main & Advanced Sample Paper JEE Main Sample Paper-42

  • question_answer
    A pistol fires a 3g bullet with a speed of 400 m/s. The pistol barrel is 13 cm long. How (much energy is given to the bullet? Also, calculate the average force acted on the bullet while it was moving down the barrel.          

    A)  140 J, 1846 N            

    B)  240 J, 184.6 N       

    C)  240 J, 1846 N            

    D)  240 J, 1746 N    

    Correct Answer: C

    Solution :

    The kinetic energy of the bullet on leaving the barrel is\[{{K}_{f}}=\frac{1}{2}m{{v}^{2}}\]\[=\frac{1}{2}(0.003){{(400)}^{2}}=240\text{J}\] The work done on the bullet is equal to the change in its kinetic energy. \[W=F\times ={{K}_{f}}-{{K}_{p}}\] where F is the average force exerted on the bullet. Thus, \[F=\frac{{{K}_{f}}-{{K}_{i}}}{x}\]          \[=\frac{240-0}{0.13}=1846N\] Initial kinetic energy is zero, since the bullet was at rest initially.


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