1. The problem statement, all variables and given/known data I have a 60kg cart on the back of my truck (travelling at 80km/h) which falls off the back and slides 45m before coming to a stop. I want to find coefficient of kinetic friction http://img9.imageshack.us/img9/4356/38603897.jpg [Broken] 2. Relevant equations Vf = 0km/h Vi = 80km/h = 200/9 m/s s = 45m using Vf^2 = Vi^2 + 2as, I find acceleration to be = - 4000/729 m/s^2 which I think is correct up to this point as the negative indicates decelleration This is where I get confused, I draw my free body diagram, which way will the force created by acceleration (i.e. F=ma) force act? Will it be to the right or to the left?