Homework Help: Dynamics- Friction

1. Oct 7, 2013

hsphysics2

1. The problem statement, all variables and given/known data

A box is halfway up a ramp. The ramp makes an angle, θ with the ground. What is the maximum value of θ before the mass will slip? μ$_{s}$=0.25

2. Relevant equations

F$_{x}$=ma$_{x}$

3. The attempt at a solution
I drew a free body diagram to show the forces affecting the box

η-mgcos=0
η=mgcosθ (eq'n 1)
F$_{x}$=ma$_{x}$
μ$_{s}$η-mgsinθ=ma$_{x}$ (sub eq'n 1 in)
μ$_{s}$(mgcosθ)-mgsinθ=ma$_{x}$
mg(μ$_{s}$cosθ-sinθ)=ma$_{x}$

I'm not sure where to go from here, or even if this is the correct path for me to take

2. Oct 8, 2013