Why does a gunman get a jerk on firing a bullet?

Why does a gunman get a jerk on a firing a bullet?

Why does a muscle get fatigued?

Why does a gun recoil on firing? Obtain an expression for recoil velocity of gun.

Why does a gun recoil When a bullet is fired ?

Why does a gun recoils when a bullet is being fired?

Why does a gun recoil when a bullet is fired from the gun ? Explain.

Why does rifle bullet get heated on striking a target ?

A rifle of 20 kg mass can fire 4 bullets /s . The mass of each bullet is 35 x 10^(-3) kg and its final velocity is 400 ms ^(-1) Then, what force must be applied on the rifle so that it does not move backwards while firing the bullets?