Question

A hockey puck of mass 0.450 kg is sliding across the ice. the puck is initially moving at 28 m/sec. however, because of the frictional force between the puck and the ice, the motion of the puck is stopped in 15.8 seconds. determine the magnitude of the frictional force.

Answer 1

Impulse is known as change in momentum, I = Change in Momentum Momentum M = m x V
  Initial Momentum = m x Vi; Final Momentum = m x Vf
 Change in Momentum = (m x Vf) - (m x Vi) = m(Vf - Vi)
 Final velocity will be 0, So Change in Momentum = -mVi
 Impulse = F x t => F x t = - m x Vi => F = (- m x Vi) / t
 => F = (- 0.450 x 28) / 15.8 = - 0.79N
 So the magnitude of the frictional force is 0.79N