(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

There is a gun which mass is M = 4 kg. The length of the gun's barrel is l = 50 cm. I need to find the average recoil force while shooting the bullet which mass is m = 5g. The speed of bullet when it leaves the gun's barrel is v = 930 m/s.

3. The attempt at a solution

Acceleration of the bullet is:

a = v^2/(2*l);

To get out of the barrel it takes time which is:

t = v/a = 2*l/v;

Theaveragemomentum of the bullet when it is in barrel is equal:

p(ave bullet) = mv/2;

But the gun gets the same average momentum (momentum conservation law):

p(ave gun) = mv/2;

So this means that the average gun's recoil force is:

F = p(ave gun)/t = mv/2 : 2l/v = mv^2/(4*l);

I am really a little bit confused. I haven't used gun's mass M in the solution. Isn't here any mistakes in the solution?

Thanks in advance.

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# Homework Help: Momentum conservation law in shooting gun problem

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