A hockey ball of mass 200 g travelling at 10 ms–1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 ms–1. Calculate the magnitude of change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.

Solution

Given, mass of the ball (m) = 200g

Initial velocity of the ball (u) = 10 m/s

Final velocity of the ball (v) = – 5m/s

Initial momentum of the ball = mu = 200g × 10 ms^-1 = 2000 g.m.s^-1

Final momentum of the ball = mv = 200g × –5 ms^-1 = –1000 g.m.s^-1

Therefore, the change in momentum (mv – mu) = –1000 g.m.s^-1 – 2000 g.m.s^-1 = –3000 g.m.s^-1

This implies that the momentum of the ball reduces by 1000 g.m.s^-1 after being struck by the hockey stick.