A hockey ball of mass $200\ g$ traveling at $10\ ms^{-1}$ 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 that occurred in the motion of the hockey ball by the force applied by the hockey stick.

Given: A hockey ball of mass $200\ g$ traveling at $10\ ms^{-1}$ is struck by a hockey stick so as to return it along its original path with a velocity at $5\ m s^{-1}$.

To do: To calculate the magnitude of change of momentum that occurred in the motion of the hockey ball by the force applied by the hockey stick.

Solution:

Here mass of the ball $m=200\ g=\frac{200}{1000}\ kg.=\frac{1}{5}\ kg.$

Initial velocity $v_1=10\ ms^{-1}$

Final velocity $v_2=5\ ms^{-1}$

Therefore, change in momentum $\vartriangle P=mv_2-mv_1$

$=m(v_2-v_1)$

$=\frac{1}{5}\ kg.\times(10-5)ms^{-1}$

$=1\ kg.ms^{-1}$