An ice skater is gliding horizontally across the ice with an initial velocity of +6.3 m/s. The coefficient of kinetic friction between the ice and the skate blades is 0.081, and air resistance is negligible. How much time elapses before her velocity is reduced to +2.8 m/s ?

Answer 1

First calculate the friction force on the ice skates. Call that F
F = M g *(0.081)
The loss of forward momentum equals the impulse, F*t
M (6.3 - 2.8) = F * t = M g *0.081* t

Note that M cancels out, so you do not need to know the mass M

t = (3.5 m/s)/[0.081*9.8 m/s^2]
= 4.4 seconds