Traveling at a speed of 17.0 m/s, the driver of an automobile suddenly locks the wheels by slamming on the brakes. The coefficient of kinetic friction between the tires and the road is 0.710. What is the speed of the automobile after 1.70 s have elapsed? Ignore the effects of air resistance.

Assuming the road is level, the force slowing the car down is given by
F = mu*N
where mu = 0.710, and since the road is level, N is the weight, m*g.

That force will cause acceleration (deceleration), a, given by
F = m*a where we know that
F = 0.710*m*g So
0.710*m*g = m*a and then
a = 0.710*g

So then plug that acceleration into
Vf = Vo + a*t
Remember that Vo and a act in opposite directions.