a bullet 8g fired from a rifle of mass 8kg moves with velocity of 400m

1.	a bullet 8g fired from a rifle of mass 8kg moves with velocity of 400m/s .find recoil velocity of rifle .
Answer» Momentum conservation: As the bullet fired is the result of internal firces inside the gun. No EXTERNAL FORCE during the process. $\implies\rm \vec{F_{ext}} = 0$ $\implies\rm \dfrac{dp}{dt} = 0$ ★ Momentum remain conserved. Initial Momentum = FINAL Momentum 0 = MV + MV $\to\rm V = \dfrac{-mv}{M}$ $\to\rm V = \dfrac{-8\times 10^{-3} \times 400}{8}$ $\to\bf V = 0.4\: (\hat{-i} )\: ms^{-1}$ ★ So, RECOIL velocity of rifle is 0.4 m/s opposite to the direction of bullet.