This problem was part of a post in another thread, but it got really messy over there and no one seems to be responding. So, here's the problem: http://www.ihostphotos.com/show.php?id=182816 And I was told this (but it didn't really help me see what to do, much): "at least it's a 90 degree angle! and frictionless ... try taking Moments around the place where the two F_N intersect did you sum F_x and F_z first?" But what forces do I sum for Fx and Fz? And where exactly is that total moment taken about? On the FBD, I drew the W force pointing straight downward from the center, as specified, then Na (Normal Force A) perpendicular to the slope on the left, and did the same, but as Nb, on the right. This part makes sense, theoretically, to me at least. But what the HECK do I add/calculate/find, etc. to get "the angle θ corresponding to equilibrium as a function of M, W, and I"??? Still don't know what exactly to do or where to start, as far as finding that.