I would appreciate any help, even a nudge in the right direction. Problem: A rectangular block of mass m was put on a triangular block of mass M. (There's a diagram for this, but imagine a right triangle, with a square on the hypotenuse, as it slides down.) Assume all friction forces can be neglected (including between the blocks and between the triangle and the surface.) What's the acceleration of the square block as it slides down, and what's the acceleration of the triangle as it slides away. I'm thinking the acceleration of the square is gsin(theta). Let the bottom left angle be theta. I know the only force on the triangle is Ncos(theta). So is the acceleration gcos(theta)?