1. The problem statement, all variables and given/known data Find coefficient of static friction if shell starts to slip at θ = 60° known - θ unknowns - P, r, Normal force, weight 2. Relevant equations friction = μ * normal force 3. The attempt at a solution I do not know where to start. It looks like the picture wants you to assume P is always horizontal so it has no effect on the normal force which means friction is constant. If friction were constant though why would it start to slip?