A flatbed tractor trailer takes off from a stop sign on a level road. If a box on the back slides back 10 meters while the truck goes forward 50 meters and attains a speed of 15 m/s, what is the coefficient of friction (μ) between the bed and the box? Assume the bed to be at least 10 meters long. FF= μFN FN= mg I don't know if those are the right formulas, specifically because no mass is given. I just don't know how to find the forces without acceleration; is there a formula for that? If these are the right formulas, how do I find the mass or FN? I chose these formulas because FF is the forward force, and it had μ in the equation. Help!!