Rotational Inertia equation help

[andrewwg94]

Homework Statement

Derive the equation for the linear acceleration of a falling mass m suspended by a string from the rim of a uniform disk of mass M and radius R that is free to rotate without friction about its principal axis.

Homework Equations

a=rα
linear acceleration = radius*angular acceleration

Torque=inertia*angular acceleration

The Attempt at a Solution

I don't really understand the question. If something is in free-fall, isn't its acceleration g? I just don't understand where the variables for the masses go. Any help is appreciated..

 

[azizlwl]

It's not a free-fall since another force acting on it, the mass m suspended by a string from the rim of a uniform disk of mass M and radius R.
http://en.wikipedia.org/wiki/Fictitious_force