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

(a) Calculation of initial momentum
Mass of hockey ball, `m_(1)`, = 200 g
`=200/1000`kg
`=0.2kg`
And, Initial velocity`v_(1)=10ms^(-1)`
So, initial momentum=`m_(1)xxv_(1)`
=0.2`xx`10
=`2 kg ms^(-1)`
(b) Calculation of final momentum
Mass of hockey ball,`m_(2)` = 200 g (Same as above)
=0.2 kg
And, Final velocity,`v_(2)=-5ms^(-1)` (Reverse direction)
So, Final momentum=`m_(2)xxv_(2)`
`=0.2xx(-5)`.....(2)
=-1kg m `s^(-1)`
Now, Chanjge in momentum=Final momentum- Initial momentum
=-1-2
=-3kg m`s^(-1)`
Thus, the change in momentum of the hockey ball is `3kgms^(-1)`.