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  3. Physics
  4. A man holding a rifle (mass of person and rifle together is 100kg) stands on a smooth surface and fires 10 shots horizontally in 5 sec. Each bullet has a mass 10 g with a muzzle velocity of 800 ms-1. The velocity which the rifle man attains after firing 10 shots will be

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Q. A man holding a rifle (mass of person and rifle together is $100kg$) stands on a smooth surface and fires $10$ shots horizontally in $5$ sec. Each bullet has a mass $10\, g$ with a muzzle velocity of $800\, ms^{-1}$. The velocity which the rifle man attains after firing 10 shots will be

VITEEEVITEEE 2019

Solution:

According to the law of conservation of momentum,
$P_{\left(inital\right)}=P_{\left(final\right)}$
$\Rightarrow mu_{1}+Mu_{2}=mv_{1}+Mv_{2}$
$\Rightarrow 0+0=10\times10^{-3}\times800+\left[100-10\times10\times10^{-3}\right]v$
$\Rightarrow v=\frac{-800}{999} \Rightarrow -0.8m/ sec$
Negative sign indicates that the velocity is opposite to the direction of bullets.