1. The problem statement, all variables and given/known data Suppose I've got a static mass on a downward plane. (For instance a car on a drive way). How would you set up this free body diagram? 2. Relevant equations F = f1+f2....etc 3. The attempt at a solution My preference is A, but I've seen it displayed in examples in my book as B. Is there and difference? In the instance of this being a mass, I used A and said W could be broken down into components of W (for Wx and Wy) and that the normal force could be broken into X and Y as well for normal and frictional forces. The problem I see is that my X components will be opposite of how they are in real life. (I.e. The weight ought to be pointing toward the left because it will roll down the plane and friction ought to be pushing it up the plane). However, if you translate the system from a normal scenario to an inclined scenario (i.e. The left sketch to A) then it ought look like A.