2. Relevant equations ΣF=m*a Ff=μ*Fn Should be it.. I gave it a shot for about the 4th time this week, my teacher said he made this up (couldn't just Google it) and that none of the other physics teachers in the school could get it. Since in my previous attempts I confused myself towards the end with numbers, I didn't substitute any numbers yet. I can't really understand the force on the large block, or the whole system for that matter so I need less of actual math help and more of just conceptual help. As far as my try goes, I usually just calculate the forces in each direction and things usually fall together but not here, I hit a point in the friction equation where I couldn't move forward, then realized that I'm not taking into account the frictionless big block.