1. The problem statement, all variables and given/known data A student pulls a box of books on a smooth horizontal floor with a force of 138 N in a direction of 23.9° above the horizontal. If the mass of the box and the books is 51.6 kg, what is the acceleration of the box? 2. Relevant equations 3. The attempt at a solution I got a force diagram. I know that Fg = 505.68N and that should be equal to Fn. I know that Ft is the force causing acceleration. What do I do from there?