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

Step 1: Given

Mass of ball$\left(\mathrm{m}\right)=200\mathrm{g}=0.2\mathrm{kg}$

The initial velocity of the ball$\left(\mathrm{u}\right)=10{\mathrm{ms}}^{-1}$

The final velocity of the ball $\left(\mathrm{v}\right)=5{\mathrm{ms}}^{-1}$

Step 2: To find

We have to find the change in momentum

Step 3: Calculation

Change in momentum$(△\mathrm{P})=$Final momentum $-$ initial momentum

$$\begin{gathered} ∆\mathrm{P}=\mathrm{m}(\mathrm{v}-\mathrm{u}) \\ ∆\mathrm{P}=0.2\times (-5-10) \\ ∆\mathrm{P}=-3{\mathrm{kgms}}^{-1} \\ ∆\mathrm{P}=3\mathrm{Ns} \end{gathered}$$

Thus, the change of momentum is $3\mathrm{Ns}.$