Length of Skid Marks: How Can I Solve This Problem?

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To determine the length of skid marks for a 1000 kg car skidding to a halt on wet concrete with a coefficient of friction of 0.60, the correct approach involves using the equation for acceleration and the kinematic equation for distance. The initial speed is 40 m/s, and the frictional force provides the necessary deceleration. The user initially miscalculated the acceleration and distance, leading to an incorrect result. Upon realizing the need to square the initial speed in the calculations, the correct skid mark length is identified as 136 meters. This highlights the importance of careful application of physics equations in solving such problems.
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Homework Statement



A 1000 kg car traveling at a speed of 40 m/s skids to a halt on wet concrete where \muk = 0.60. How long are the skid marks?



Homework Equations



Vf = Vi + 2ad
fk = \mukN = ma



The Attempt at a Solution


This problem is driving me crazy. Nowhere in the book does it tell you how to do this or even a similar problem. Plus, online, all I can find is how to find the speed once you've found the length of the skid marks! And yes, I tried doing the problem in reverse but the answer never comes out right.

Here is what I've done.

1000 * 9.8 = 9800
9800 *.6 = 5880
acceleration = 5880/1000 = 5.88

0 = 40 + 2 * 5.88 * d
d = 3.4

I know I've done something incredibly wrong here because the answer in the back of the book is 136!

I appreciate the help

a(1000) = 5800
 
Physics news on Phys.org
0 = 40 + 2 * 5.88 * d

That 40 should be squared!
 
oh wow. thank you so much!
 

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