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

A box of textbooks of mass 24.5 rests on a loading ramp that makes an angle with the horizontal. The coefficient of kinetic friction is 0.260 and the coefficient of static friction is 0.360.

As the angle is increased, find the minimum angle at which the box starts to slip.

**2. Relevant equations**

N+f

_{s}+W=0

N=mg cos[tex]\vartheta[/tex]

f

_{s}=mg sin[tex]\vartheta[/tex]

**3. The attempt at a solution**

In my notes, it gives an example of an object at rest on an inclined plane and sets up the two above equations with the angle and weight of the object both given. The problem is that when I add up the three forces N, f

_{s}, and W I do not get "0". This is leaving me quite confused.

I have tried substituting the equations above into the top equation equal to zero, but I cannot figure out how to solve for theta since Weight is involved.

Can anyone give me a push in the right direction. I feel like I am forgetting something.