Where did you find the expression? In general, when studying basic physics, you aren't supposed to find expressions; instead you are expected to derive expressions from expressions already established. If you do not understand where the "found" expression comes from, then it is easy to use it incorrectly.

I found an expression for the ball's angular velocity (w) in terms of R, g, and y (y is the ball's height, as shown in the picture)I was wondering what the radius of the circle travelled by the ball is at height y. Not sure if that plays in a role in your problem.

and the expression is: w = sqrt(g/(R-y))