Chapter 8

NCERT
Class 9
Science
Solutions
12. A hockey ball of mass 200 g travelling at 10 ms–1. It struck by a hockey stick so as to return. It along it's original path with a velocity at 5 ms–1. Calculate the change of momentum occurred in the motion of the hockey.

Question:

A hockey ball of mass 200 g travelling at 10 ms–1. It struck by a hockey stick so as to return. It along it's original path with a velocity at 5 ms–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 u = 10 ms–1

final velocity of ball v = 5 ms–1

initial momentum of ball = mu

                                        = 0.2 × 10

                                        = 2 kgm/s

final momentum of ball = mv

                                       = 0.2 × (–5)

                                       = –1 kgm/s

Change in momentum = mv – mu

                                      = –1 – 2

                                      = –3 kg-m/s

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