Calculate the recoil velocity of a gun having mass equal to 5 kg, if a bullet of 25 g acquires the velocity of 500 ms−1 after firing from the gun.
Given, mass of bullet (m1) = 25 g = 0.025 kg
velocity of bullet before firing (u1) = 0
velocity of bullet after firing (v1)=500 ms−1
mass of gun (m2) = 5 kg
velocity of gun before firing (u2) = 0
Let velocity of gun after firing be v2
From law of conservation of momentum, m1u1+m2u2 = m1v1+m2v2
⇒ v2=−12.55=−2.5 ms−1
Thus, recoil velocity of gun is equal to 2.5ms−1. Here, the negative(- ve) sign shows that gun moves in the opposite direction of bullet.