Question

A hockey ball of mass `200g` travelling from west to east at `10m//s` is struck by a hockey stick. As a result, the ball gets turned back and now has a speed of `5m//s`. If the ball and hockey stick were in contact for `0.2s`, Calculate
(i) initial and final momentum of the ball
(ii) rate of change of momentum of the balll
(iii) force exerted by hockey stick on the ball.

Answer 1

Here, `m=200g = 0.2kg, u=10m//s` west to east, `v= -5m//s`, east to west, `t=0.2s`.
(i) Initial momentum of ball `=m u = 0.2xx10= 2kg m//s` , from west to east.
Final momentum of the ball `=mv=0.2(-5)= -1 kgm//s` , from east to west.
(ii) Rate of change of momentum of ball `=("final momentum -i nitial momentum")/("time taken")=(-1-2)/(0.2)`
(iii) Force exerted by hockey stick on the ball = rate of change of momentum of ball
`= -15kg m//s^(2)= -15N` from east to west.