A hockey ball of mass 200 g travelling at 10 m s^–1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 m s^–1. Calculate the magnitude of change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.

Mass of ball m = 200g = 0.2 kg
Initial velocity of ball u =10ms⁻¹
Final velocity of ball v=5ms⁻¹
Therefore, change in momentum 

(△p) = Final momentum - initial momentum                       

△p  =  mv - mu = m(v−u) 

       = 0.2×(−5−10) 

       = −3 kgms⁻¹

         = −3 Ns.

Hence the magnitude of change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick is −3 Ns.