Question

what is linear momentum of bullet and gun on firing

Answer 1

Consider the gun and bullet in its barrel as an isolated system
In the begining when bullet is not fired both the gun and bullet are at rest.So the momentum of the before firing is zero
pi=0
Now when the bullet is fired ,it moves in the forward direction and gun recoil back in the opposite direction
Let mb be the mass and vb of velocity of the bullet And mg and vg be the velcoity of the gun after the firing
Total momentum of the system after the firing would be

pf=mbvb +mgvg

since no external force are acting on the system,we can apply the law of conservation of linear momentum to the system
Therfore
pf=pi
or mbvb +mgvg=0
or vg=-(mbvb/mg)