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

[wcbryant87]

Homework Statement

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

Homework Equations

Vf = Vi + 2ad
fk = $$\mu$$_kN = 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

 

[hage567]

0 = 40 + 2 * 5.88 * d

That 40 should be squared!

 

[wcbryant87]

oh wow. thank you so much!