1. The problem statement, all variables and given/known data A car and pulley system are setup as shown. Find the acceleration of the car. The car wheels have a friction coefficient of 0.15. The car has a mass of 0.05 kg while the block has a mass of 0.02 kg. http://sadpanda.us/images/836771-GBD7SB9.jpg [Broken] *sorry if the picture is bad I tried to sketch it quickly on paint. I chose up and right to be positive. 2. Relevant equations Fnet = ma Ff = μFn Fg = ma 3. The attempt at a solution If we draw two seperate free body diagrams we would get the following forces. Car: Force gravity is 0.49 N Fg = ma = 0.05 * 9.8 = 0.49 N and since the car isn't accelerating vertically the normal force is the same but opposite direction. Ff = μFn = 0.49 * 0.15 = 0.0735 N We also have a tension in the rope that we don't know. Block: Force gravity is 0.196 N. Fg = ma = 0.02 * 9.8 = 0.196 N We also have the tension of the rope which we again don't know. To calculate the acceleration of the car: Fnet = ma Fgcar + Fncar + Ff + T1car + T1block + Fgblock = ma Since forces cancel out. Ff + Fgblock = ma -0.0735 - 0.196 = (0.02 + 0.05) * a -0.2695 = 0.07 * a a = -3.85 a = 3.85 m/s^2 [Down] I have a feeling something is wrong because in the previous question it said there was a frictionless surface and I ended up getting 2.8 m/s^2 for the acceleration which is lower. I'd assume a frictionless surfaces would cause there to be a higher acceleration. If anyone can verify this for me and tell me what I'm doing wrong it'd be much appreciated.