Check for collision of ball in a circular path and a stationary object on the path for iPhone app

Question

I have set a ball on a circular path by animating its layer. When i checked for collision with another object, I tried use CGRectIntersectsRect but to no avail.

What is the difference between a layer and the frame? I suspect that the frame is not following the layer animation hence CGRectIntersectsRect is not something that I should be using.

Is there any other way for me to check for collision?