question_answer 13)

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

Answer:

Mass of ball (m) = 200 g = 0.2 kg Initial velocity of ball (u1) = 10 m s-1  Initial momentum of ball =mu1 = 0.2 kg x 10 m s-1 = 2 N s Final velocity of ball (u2) = - 5 m s-1 (Minus sign denotes that ball is moving in opposite direction.)  Final momentum of ball =mu2 = 0.2 kg x -5 m s-1 = -1 N s  Change in momentum = Final momentum - Initial momentum = - 1 N s - 2 N s = - 3 N s. Minus sign denotes that change in momentum is in the direction opposite to the direction of initial momentum of the ball.