How to Determine Angular Acceleration from Given Equations?

[depre87]

Homework Statement

http://imageshack.us/photo/my-images/855/10544781.png/

Homework Equations

a=[r''-r0'^2]er+[r0'' + 2r'0']e0 where 0 = theta

The Attempt at a Solution

stumped about it, I've tried setting the above to 0 then work out r which is 200 m but that's just cluelessly subbing values into the equation, any directions as to where to head? thanks!

 

[ehild]

The car moves along the road with constant velocity v. Find x as function of time. Find how θ and $\dot {\theta}$ are related to v and time.

ehild