Two billiard balls $A$ and $B$, each of mass $50 g$ and moving in opposite directions with speed of $5 {\mathrm{ms}}^{-1}$ each, collide and rebound with the same speed. The impulse imparted to each ball is 

Initial momentum of ball $A=\left(0.05\right)\left(5m{s}^{-1}\right)=0.25kg m{s}^{-1}$
As the speed is reversed on collision, Final momentum of the ball $A=\left(0.05kg\right)\left(-5m{s}^{-1}\right)=-0.25 kg m{s}^{-1}$
 Impulse imparted to the ball $A=$ Change in momentum of ball $A=$Final momentum $-$ Initial momentum $=-0.25 kg m{s}^{-1}-0.25 kg m{s}^{-1}=-0.5 kg m{s}^{-1}$

Similarly, initial momentum of ball $B=\left(0.05kg\right)\left(-5 m{s}^{-1}\right)=-0.25 kg m{s}^{-1}$
Final momentum of ball $B=\left(0.05kg\right)\left(5 m{s}^{-1}\right)=+0.25kg m{s}^{-1}$
Impulse imparted to ball $B=\left(0.25 kg m{s}^{-1}\right)-\left(-0.25 kg m{s}^{-1}\right)=0.5 kg m{s}^{-1}$
Impulse imparted to each ball is $0.5 kg m{s}^{-1}$ in magnitude. The two impulses are opposite in direction.