1. The problem statement, all variables and given/known data a block is sliding down an inclined plane that is resting on a frictionless terrain. so as the block slides down the ramp, the ramp also moves. Calculate the force exerted by the block on the plane. I have the mass of both the object and the plane as variable m and M, the angle of contact theta, and using Lagrangians (or is it Hamiltonians... I am not quite sure at this point of the difference. feel free to explain that to me for extra credit lol :) but using L = T-U I have found the equation for the acceleration of x and X. 2. Relevant equations f=ma 3. The attempt at a solution I am thinking that I just need to say F=ma. the force required to accelerate the the inclined plane to the left is its mass M times its acceleration. That will give me the x component of the Normal Force acting on the Inclined plane by the block. Then using trigonometry, I can solve for the Normal Force. and I believe that is what the problem is looking for. I am not entirely sure though. a little voice in my head is telling me that that is too easy. that maybe the mass of the little block should also be a factor in calculating the required force. (the mass is present in the equation of acceleration btw, but I am not sure if it should be part of the m in the F=ma equation.). What do you think? is my first impulse a very wrong oversimplification... or is it fine?