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.

A hockey ball of mass `200g` travelling from west to east at `10m//s`

1.	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» 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.