How Does Friction Affect Torque in an Atwood Machine?

[AnotherStuden]

Homework Statement

Two masses are suspended from a pulley of mass m supported by an axle (Atwood machine).
What is the net torque acting on the pulley wheel in terms of T1 and T2?

There is friction between pulley and rope.
Ropes are massless and pulley can rotate without friction about its own wheel.

Homework Equations

τ = I*α

The Attempt at a Solution

This is what I got so far:
http://img685.imageshack.us/img685/4333/24667502.th.png

Others get τnet = (T1-T2)r
Why??

Thanks in advance!

 

[AnotherStuden]

Wait nevermind, I just realized that both tensions should be pointing downward.

So, (T1-T2)=r is correct.

Thanks anyways!