1. The problem statement, all variables and given/known data An object of mass M=10kg is being pulled up by a system of pulleys. a)What force do you need to exert on point A for the object to move uniformly ? b) What force do you need to exert on point A, if the friction in each of the pullies is 0,5N and the pulleys are not massless - the mass of the 1st one is 100g, the 2nd - 200g, the 3rd - 300g, the 4th- 400g. http://img148.imageshack.us/img148/5526/unledbde.jpg [Broken] Uploaded with ImageShack.us 2. Relevant equations 3. The attempt at a solution I solved the A part quite easily, got a result of F=12,5N, but i'm stuck with part B - i can't figure out the directions of the friction forces .