(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?

Asked by Arkajyoti Banerjee | 20th Sep, 2014, 05:43: PM

Expert Answer:

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

Answered by Jyothi Nair | 21st Sep, 2014, 12:07: PM

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