Ok, so I have a problem in which an object is thrown tangentialy to a surface which makes 45o with the orizontal. So we know, that there is an MOMENT OF FORCE, an instant acceleration, which give the object the initial velocity : Vo. The object is thrown in the upside direction(so is slowing down). Now, we know the friction between the object and the surface (u=0.25). The problem now is asking for the object's acceleration... I am quite good at other kind of problems concerning Newton's Physics but this is blowing my mind :grumpy: , I don't know how to translate the initial velocity into a force, in order to do my basic rutine :). Thx!