Find Coeff. of Static Friction of Car on Track

[wmrunner24]

Homework Statement

A car traveling on a flat circular track of radius 5m accelerates uniformly from rest with a tangential acceleration of 1.7m/s^2. The car makes it 0.2 of the way around the track before skidding off. Acceleration of gravity=9.8m/s^s.
What is the coefficient of static friction between the car and the track?

Homework Equations

F_c=V^2m/r
F=ma

The Attempt at a Solution

So I tried this:
F_c=F_f
V^2m/r=$$\mu$$mg
v^2/gr=$$\mu$$

To determine the velocity at which the car slips, I said V^2=2ax, where x is 2$$\pi$$r/5.

So I get 4$$\pi$$a/5g=$$\mu$$

It's not correct. Why is that?

 

[Delphi51]

Nice solution. I get 0.436, but I'm prone to calculation errors.

 

[wmrunner24]

The online homework system marks it wrong. I can't explain it. Is there another way to do this?