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; The average momentum 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.