What is the orientation of the vector of friction?

[JrK]

I have a question about the direction of the graphical method. I built all the drawings with the final position back to the initial, why ? (at the beginning of the thread I done that, without think of the direction) the true direction is from the initial position to the final. If I drew from the initial to the final I have less than d2, it is worst: I have less than d2. With basic examples, it is easy and from initial to final or the reverse it is the same result, here not at all.

 

[A.T.]

With basic examples, it is easy and from initial to final or the reverse it is the same result, here not at all.

If you get different diagrams depending on what part you draw first, then that's more a problem with your consistency, rather than physics.