Kleppner and Kolenkow - Pulleys

[jgens]

Homework Statement

Masses M₁ and M₂ are connected to a system of strings and pulleys as shown. The strings are massless and inextensible, and the pulleys are massless and frictionless. Find the acceleration of M₁.

http://img844.imageshack.us/img844/3758/cimg0572.jpg

Homework Equations

N/A

The Attempt at a Solution

I've reasoned that since the pulley is massless, the net force acting on it must be zero (otherwise the acceleration would be infinitely large). I could then use the tensions in the strings to arrive at an answer for the acceleration of M₁, but I'm not sure that my reasoning really applies here. Could someone please offer some guidance?

 

[jgens]

This was falling towards the bottom of the page, so I just wanted to bump it before it actually fell off.

 

[maphec]

Hi, did you ever get a solution or an approach to this problem? I am also working on the same one right now and am stuck on it...