Ahockey 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.

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