Mass of the hockey ball, m= 200 g = 0.2 kg

Hockey ball travels with velocity, v_{1}= 10 m/s

Initial momentum = mv_{1 }

Hockey ball travels in the opposite direction with velocity, v_{2}= -5 m/s

Final momentum = mv_{2 }

Change in momentum = mv_{1}- mv_{2}= 0.2 [10 - (-5)] = 0.2 (15) = 3 kg m s^{-1}

Hence, the change in momentum of the hockey ball is 3 kg m s^{-1}