Free body diagrams for system A that consists of two blocks and for system B with one block: http://i7.photobucket.com/albums/y260/filipina4eva92/1329082077750.jpg acceleration and net force from the systems: http://i7.photobucket.com/albums/y260/filipina4eva92/Unknown.jpg frictional force: http://i7.photobucket.com/albums/y260/filipina4eva92/Unknown2.jpg I'm having a hard time understanding how a free-body diagram works. I know that each of the diagrams for the two systems have to have weight, normal force, and friction acting on it, but I don't completely understand the concept behind them. And I don't even know where to begin with the other two parts of the question. Please help! I'm more than willing to understand all of this. Thank you!