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

A uniform ladder of mass m and length l leans at an angle theta against a frictionless wall. If the coefficient of static friction between the ladder and the ground is mu, determine a formula for the minimum angle at which the ladder will not slip.

**2. Relevant equations**

**3. The attempt at a solution**

I know how to create the free body diagram and use the rules for static equilibrium in the x and y direction, but I don't know why the torque equation is set up as: W(lsin(theta))-(1/2)(lmgcos(theta)) = 0 where W is the Force exerted by the wall and mg is the Force due to gravity acting on the ladder at the center of its mass. Mainly, where do the sin and cos come from when the the wall force is parallel and gravity perpendicular to the ground. I know it has something to do with the ladder being at an angle, but I can't wrap my mind around where they exactly came from. Also, it's a frictionless wall which makes me believe that the wall force should not have any components. Thanks in advance.