# Friction and Acceleration problem?

1. Oct 10, 2011

### bman123

1. Traveling at a speed of 15.8 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 0.760. What is the speed of the automobile after 1.10 s have elapsed? Ignore the effects of air resistance

2. Ffr=(mu)(FN)
FN=(mass)(g)

3. There is no mass to calculate the normal force. I tried multiplying the acceleration times the friction coefficient and dividing that by the time elapsed but can't get the right answer. ANy help?

2. Oct 10, 2011

### praharmitra

Well, friction = $$\mu m g = -m a \implies a = -\mu g$$.

Now can you use ordinary kinematics to get the rest of the answer?