A shell of mass 0.01 kg fired by a gun of mass 10 kg. If the muzzle speed of the shell is 50 ms–1, what is the recoil speed of the gun?

If v be the recoil speed of the gun and u be the muzzle speed of the shell, then as momentum of the system is conserved, we can write Mv + m(v - u) = 0 ⇒ V = mu/(M + m). V = 0.01 x 50 / (10 + 0.01) = 0.05m/s