1. The problem statement, all variables and given/known data We have a 200-LB door hanging from 2 rollers, A & B, which are 5 feet apart. Coeffs of friction for A and B are .15 and .25, respectively. A force P is applied to the door. How big must it be to move the door to the left? 2. Relevant equations 3. The attempt at a solution I have included a FBD. The downward force is the 200LBs, so the normal force would be 200, or 100 at each roller. That's reasonable, since the whole thing is symmetrical. The forces in x direction are P (to the left) and the total of muAN and muBN to the right. So here we go: Sum of forces in x: -P + (.15)(100) + (.25)(100) = 0 This yields a value of 40 for P. The book's answer is 45.5 Hmmm....been struggling with this for a week. Not sure where I made a wrong turn. Any help appreciated. Thank you.