Two stacked boxes and a pulley with a weight attached

[donveppy]

Homework Statement

The system shown is released from rest. Mass one (0.450 kg) rests on mass two (0.820 kg) and the coefficient of static friction between the two masses is 0.560 and the same for the mass and the table. Determine the maximum mass for M3 such that the mass one will not slide on mass two. The string can be considered massless and the pulley is frictionless

Homework Equations

fs=uk(n)
sumF=M(a)

The Attempt at a Solution

.450(9.8)(.560)= 2.46N static friction force between block one and two

(.450+.560)(9.8)(.560)= 6.96N static friction force between both blocks stacked and table

T-(6.96N)=M(1+2)(a) sum forces x direction

w2- T=M2(a) sum forces in y direction

 

[BvU]

System shown ? Shown where ?

Oh, and: welcome to PF!

Tip: don't write calculations with numbers. Instead write expressions with variables and work with those. Only at the last step fill in values (i a numerical answer is required).