Discussion on: Problem 522 | Friction

For the 200 lb block he uses rotation of axis. For N₂ as the y-axis and along incline will be the x-axis. we get the equation for N₂ using summation of forces along y-axis. The degree of the strut with respect x-axis is 15 degrees as you subtract (60^o - 45^o) just extend a line for strut to the incline plane then draw a vertical line where the strut and the incline pane intersect then use your basic trigo analysis. :)))

I hope this will help you :)))