1. The problem statement, all variables and given/known data A cup of coffee is sitting on a table in an airplane that is flying at a constant altitude and a constant velocity. The coefficient of static friction between the cup and the table is 0.30. Suddenly, the plane accelerates, its altitude remaining constant. What is the maximum acceleration that the plane can have without the cup sliding backward on the table? 2. Relevant equations fs(max) = coefficient of friction * normal force Normal force = Work = mass * acceleration 3. The attempt at a solution It doesn't give a force, work, or mass. All I can do is look at equations with 2 or 3 unknown variables. In addition to help with this problem, does anyone have any suggestions on solving problems that seem to be missing information? I'm coming across a lot of them and there's nothing worse than being stumped before even attempting to solve.