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

Explanation

Mass of ball (m) =`200g=0.2kg`
Initial velocity of ball `(u_1)=10ms^-1`
`therefore` Initial momentum of ball =`mu_1`
`=0.2 kg times 10 ms^-1=2 Ns`
Final velocity of ball `(u_2)=-5 ms^-1`
`therefore` Final momentum of ball =`mu_2`
`=0.2 kg times -5 ms^-1=-1 Ns`
`therefore` Change in momentum
=Final momentum- Initial momentum
`=-1Ns-2Ns=-3Ns`
MInus sign denotes that change in momentum is in the direction opposite to the direction of initial momentum of the ball.