You forgot to specify the mass of the car.
Anyway, this is a possible approach, having the mass:
1) Draw a free body diagram.
2) Convert the velocity from mph to m/s.
3) Find the deceleration of the car.
This deceleration is due to the sliding friction force (look at the FBD) which you can easily find:
Ff = μN
And N in this case is simply mg (you can see this in your FBD).
After you have found Ff, you can find the deceleration applying Newton's 2nd Law:
F = ma
4) At this point you have the initial velocity, the final velocity (0m/s, since the car stops), and the deceleration. You can apply kinematic equations to find the distance traveled.
In the second part you just have a different coefficient of friction. You can repeat the whole process from step 3, and find the distance.
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Last edited by Roller; Sep 26th 2015 at 12:23 PM.
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