Here, mass of bullet, `m_(1)= 10g= 10xx10^(-3)kg= 10^(2)kg`, mass of gun, `m_(2)= 5kg`
velocity of bullet, `v_(1) = 400m//s`, speed of recoil of gun `v_(2) = ?`
As total momentum of bullet and gun after firing = total momentum before firing, `m_(1)v_(1)+m_(2)v_(2)=0`
or `v_(2) = -(m_(1)v_(1))/m_(2)= -(10^(-2)xx400)/5` or `v_(2)= -0.8m//s`
Negative sign shows that the gun moves in a direction opposite to that of the bullet.
