unwounding spool of wire

[cryptoguy]

1. The problem statement, all variables and given/known data
A spool of wire mass M and radius R is unwound under a constant force F. Assuming the spool is a uniform solid cylinder that doesnt slip, show that the acceleration of center of mass is 4F/3M


2. Relevant equations
\tau = I\alpha = F*R


3. The attempt at a solution

Here's what I got, not sure if this is right.
\tau_{}net = \tauF - \tauFfric
I\alpha = F*R - Ffric*R
.5MR^2(a_{cm}/R) = F*R - Ffric*R

a_{cm} = (F-Ffric)/.5M

The problem is that I don't know Ffric (Friction force).

Thank you in advance for help

[awvvu]

Use F = ma on the spool to get another equation, this should allow you to eliminate F_fric.