Deriving RPM for Object Slipping from Rotating Surface

[icanletyougo]

Homework Statement

A object(have mass M1) is placed at a R1 distance from the center of a horizontal surface that can rotate. The surface rotation is very FAST INCREASE ( tangential acceleration is non-negligible) until the surface reaches a cirtical rotation rate. At that instant, the object begins to slip with respect to the surface. Derive an expression for number of rotation per minute made by the surface at this critical time.

Homework Equations

The Attempt at a Solution

I have no idea...Can somebody give my a hint? thank you

 

[gneill]

What holds the block in place? What forces are operating? What are their directions?