Minimum Kinetic Friction for Inclined Block System

[ISU20CpreE]

I have a block conected to another block by a string in an inclined surface, with a frictionless pulley. Both blocks are the same weight so i already figure the acceleration of the object that its being pulled up.

What I don't know is how can I calculate the minimum kinetic friction that will keep the system from accelerating.

I tried setting the acceleration to zero for this formula:

$$a= 1\ frac{m2*g-m1*g*sin\theta - \mu*m1*g*cos\theta} {m1+m2} [\tex]<br /> <br /> after that i really don't get the answer. Please any sugestions.$$

 

[Fermat]

Already answered in the other thread

 

[ISU20CpreE]

thanks fermat