Variably Solving for Minimum Tangential Speed

[CandyApples]

Homework Statement

A ride at a carnival rotates about a vertical axis. When spinning fast enough the bottom is dropped and the rider sticks to the side. Find the minimum tangential speed so that the rider does not fall. R=radius of circle, u= coefficient of static friction and g represents gravity. The answer must be in these terms.

Homework Equations

F = ma
F = un
Ca = v^2/r

The Attempt at a Solution

V = sqrt (Ca*r)

I think I am missing something here, as it is not with respect to the right variables. Any hints on what to do next, or if I am heading down the wrong path?

 

[rl.bhat]

What is the normal reaction of the surface?
In which direction the frictional force acts?
What should the condition so that rider does not fall?