A friend of mine gave me this problem, and it was somewhat hard: A rectangular block of mass M1 rests on a horizontal table. Masses M2 and M3 are free to slide along the surfaces of M1 and are attached by a massless string over a frictionless pulley. For the diagram, go to: http://img451.imageshack.us/img451/7456/28142628dx2.jpg Also, assume all surfaces are frictionless. a) Draw free body diagrams for M1 and M2. Assume the pulley makes a 45 degree angle with the horizontal. b) Find the external force F that should be applied to M1 so that M3 will stay at a fixed height above the table. (meaning M2 and M3 dont move relative to M1) c) Suppose there is no external force. All masses are held fixed up until time t=0, and then they are released. Find the initial tension in the string T, and the initial acceleration a of M1 just after being released. Express the answer in terms of the masses given and g. My thoughts so far: For a), on M1, I drew the normal force it had with the table and the gravitational force. Do I need to draw some sort of normal force for the contact it has with M3? The M2 diagram has its normal force with M1, gravity, and the tension force to the right. For b), I thought the force would be M3*g, because that is the tension force, so applying that force would somehow counter it? It is somewhat of a wild guess, and I am pretty sure it is incorrect, b/c that seems too easy. For c), I don't see how how M1 would even accelerate, nor do I see how the "initial" tension would ever change after time.