Question

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 1

Mass of ball (m) = 200 g = 0.2 kg

Initial velocity of ball (u₁) = 10 ms^-1

∴ The initial momentum of the ball = mu₁

= 0.2 kg × 10 ms^-1

= 2 N s

Final velocity of ball (u₂) = - 5 ms^-1

(The minimum sign denotes that the ball is moving in the opposite direction.)

∴ Final momentum of ball = mu₂

= 0.2 kg × (- 5 ms^-1)

= - 1 N s

∴ Change in momentum = Final momentum - Initial momentum

= - 1Ns - 2Ns

= - 3Ns

The Minus sign denotes that the change in momentum is opposite to the direction of the initial momentum of the ball.