(i) A ball was moving at a velocity of 10m/s from rest and its mass is 200g. suddenly it was struck by a hockey stick which made it return along its original path at the velocity of 5m/s. What amount of impulse did act on the ball?

Given that:

The mass of the ball = 200 g =0.2 kg,

Initial velocity of the ball , u = 10 m/s

After being struck by a hockey stick the velocity changes to 5 m/s.

i.e. Final velocity of the ball , v = - 5 m/s (- ve sign as the the ball goes in the direction opposite to that of the initial direction of motion of the ball)

We know that impulse  = change in momentum

Initial momentum of the ball, mu = 0.2 kg × 10 m/s = 2 kg m/s

Final momentum of the ball after being struck by the hockey stick , mv = 0.2 kg× -5 m/s = -1 kg m/s

Impulse = change in momentum

             = mv - mu

             = -1 kgm/s -2 kgm/s

             =-3 kg m/s 

             =-3 Ns

- ve sign indicates that the force is exerted in the opposite direction of initial velocity