How to detect collision while moving object in Acceleration is on (iPhone)

Question

Hi All,

I have to move the ball in specified path, lets say a circular road with the help of Accelerometer. I am able to move the ball using UIAccelerometer. But i am confused how i will move the ball on circular road or on any other shape. How i will detect collision so that ball will only move in the specified area(road) and will not move out of the road

Thanks in advance.

Regards, Vishal