I was working the following problem: Two blocks rest on a horizontal frictionless surfce (the top block being 5kg and the bottom block being 10 kg). The surface between the top and bottom blocks is roughened so that there is no slipping between the two blocks. A 30 N force is applied to the bottom block ( a 30 N horizontal force). What is the force of static friction between the top and bottom blocks The answer key tells me that the answer to the problem is 10 N. I know that fsMAX = coefficednt of static friction * FN. I figured that the normal force for the top block is 49 N and the bottom block is 147 N. I can't figure out what combination of those numbers equal 10 N. Any help would be appreciated.