Finding rotational inertia of a yo-yo

[chaose]

A yo-yo shaped device mounted on a horizontal frictionless axis is used to lift a 30kg as shown. The outer radius R of the device is 0.50m, and the radius r of the hub is 0.20 m. Wen a constant horizontal force F of magnitude 140N is applied to a rope wrapped around the outside of the device, the box, which is suspended from arope wrapped around the hub, has an upward acceleration of magnitude 0.80 m/s^2. What is the rotational inertia of the device about its axis of rotation?

http://img438.imageshack.us/img438/7076/problemci9.jpg

 

[Doc Al]

Well... where's your work?

Hint: Apply Newton's 2nd law to both the yo-yo and the box. Take advantage of the information given and you'll be able to solve for the rotational inertia.