1. The problem statement, all variables and given/known data A farmer hitches her tractor to a sled loaded with firewood and pulls it a distance of 20m along level ground. The total weight of sled and load is 14700N. The tractor exerts a constant 5000N at an angle of 36.9 above the horizontal. There is a 3500N friction force opposing the sled's motion. Find the work done by each force acting on the sled and the total work done by all the forces. 3. The attempt at a solution To start off, I found the work done by each force. I drew the figure as follows: http://img254.imageshack.us/img254/3663/49497726xp3.jpg [Broken] my calculations cos(angle) = x/5000 5000 cos 36.9 = 3998.42 (3998.42J)(20m) = 79968.47 and 3500cos180 = -3500 (-3500J) (20m) = -70000 79968.47-70000 = 9968.47 My answer: 9968.47 Book answer: 10000 Is my process wrong, if so where did I go wrong? Don't the gravity and normal force cancel out? From my reading in the book, we suppose to only count the horizontal forces, which is what I did here.