Kinematics of a Particle Tangent-Normal components

[teknodude]

Homework Statement

http://img136.imageshack.us/img136/1930/carrs8.th.png

Homework Equations

a = (v^2/p) en + (v*)et
a- accel
v-velocity
en- inward normal
et- unit vector along tangent
v*- tangential acceleration
p- curvature

The Attempt at a Solution

FOr the first part I just need to find the velocity using the above equation. Since velocity is constant a =0. Therefore tangential accel (at) = 0.4g.
Then just solve for v. Now they gave us the dimensions of the car, so I guess I can't treat the car as a just a particle. The TA just told us to subtract the curvature from the given dimensions,BUT why are we doing that?

so curvature = 120m - 0.6

 

[doodle]

I believe the adjustment is made because the center of gravity of the car is slightly above the road surface.