1. The problem statement, all variables and given/known data A small block of mass m rests on the rough, sloping side of a triangular block of mass M which itself rests on a horizontal frictionless table as shown in the figure. http://s7.photobucket.com/albums/y252/mikey555/?action=view¤t=GIANCOLIch05p033.jpg (edit: image doesn't appear. it's here:http://s7.photobucket.com/albums/y252/mikey555/?action=view¤t=GIANCOLIch05p033.jpg) If the coefficient of static friction is [tex]\mu[/tex] determine the minimum horizontal force F applied to M that will cause the small block m to start moving up the incline. 2. Relevant equations Newton's 2nd law for each individual block. 3. The attempt at a solution So first I drew FBDs for both blocks. - For the small block, there's a frictional force to the right, its weight downward, and a normal force on M on m upward. - For the wedge, its weight downward, the normal force of the ground on M upward, an applied horizontal force towards the right, and the normal force from m perpendicular to the ramp of the wedge. I think there might be a force on each that I'm missing. Is there a frictional force back on the wedge from the small block? Also, is there a force pushing the small block up the ramp? Where I get confused is how to form the equations for x- and y-directions. I need to make an F=ma equation for the horizontal direction of the small block to find out how much external force on the wedge is required for it to move up the ramp, except I don't know which way acceleration is going. And if I'm trying to find out how much force is required to break m's static friction, then won't it not be accelerating in either direction (instantaneously still)? So basically I'm stuck after making my FBDs. Obviously there's a slough of questions here and I don't expect anyone to answers them all. But I would appreciate it very much if someone could give me some direction on where to go after I make FBDs (and if I have any mistakes on mine!). Thank you!