The question is: "Two blocks are accelerated across a horizontal frictionless surface as shown. Frictional forces keep the two blocks from sliding relative to each other, and the two move with the same acceleration. What is the magnitude of the horizontal component (frictional force) of the force exerted on the small block by the large block?" The mass of the small block on top is: M ,the mass of the bottom block is: 2M , and the force, P is: 3 N. I drew the FBD's, block M has three forces: n1 (up), Mg (down), and f (right). Block 2M has 5 forces??? P (right), 2Mg (down), n1 (down), n2 (up), and f (left). I can't seem to get it, there appears to be too many unknowns to me. I appreciate any help. Thanks!