(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

You have been called to testify as an expert witness in a trial involving an automobile accident. The speed limit on the highway where the accident occurred was 40 mph. The driver of the car slammed on his brakes, locking his wheels, and left skid marks as the car skidded to a halt. You measure the length of these skid marks to be 219 ft, 9 in., and determine that the coefficient of kinetic friction between the wheels and the pavement at the time of the accident was 0.400.

How fast was this car traveling (to the nearest number of mph) just before the driver hit his brakes?

2. Relevant equations

I would guess using the old formula of x1-x0 = (Vf^2-Vi^2)/2a would work. I am not sure how to find a though.

3. The attempt at a solution

0-66.9798 (that is the 219.75 ft converted to meters) = (0 - Vi^2)/2a

I am not sure where to go from here; please help! I know the answer is 51.2 mph, but I am lost on where to go.

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# Homework Help: Kinetic Friction to find velocity

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