1. The problem statement, all variables and given/known data Hi everyone, I have a problem that has me stumped and would appreciate some pointers as to where I am going wrong and maybe point me in the right direction for solving the problem. The problem is in essence to use the "Work-Energy Theorem" to find the co-efficient of kinetic friction in a pulley system. Problem - We have an 8.00 kg-block on flat horizontal tabletop attached via a rope and pulley to a hanging 6.00 kg-block. The rope and pulley have negligible mass and the pulley is friction-less. Initially the 6.00 kg-block is moving downward and the 8.00 kg-block is moving to the right, both with a speed of 0.900 m/s. The blocks come to rest after moving 2.00 meters. Use the Work-Energy Theorem to calculate the coefficient of Kinetic friction between the 8.00 kg-block and the tabletop. 2. Relevant equations Main equations I used to attempt to solve this problem were .. Work = Change in Kinetic energy Work = Force x Distance (for a constant force) I used these separately for each of the masses (blocks) connected by the pulley system. 3. The attempt at a solution Basically I used the two main equations of the Work-Energy Theorem to try to solve this. I first calculated the Work used in moving each block using the difference in kinetic energy over the distance travelled that is ... W= K(2) - K(1) = 1/2 mv(2) sqrd - 1/2 mv(1) sqrd for each block, and since both blocks come to rest, each of the equations above reduce to just 1/2mv(1) sqrd for each block. I then took the difference in the values for the work each block expended to be the work expended by friction force. Now since (for a constant force) WORK also equals Force x distance, I equated the Work difference above to be equal to the work expended by the Kinetic Friction Force. And so Work difference = Work(Friction force)=Kinetic friction x distance moved. From my calculations I got W(8kg-block)=3.24 J, W(6kg-block)=2.43 J giving difference of 0.81 J as the Work of Friction force. Now since W=f x distance then f=w/distance =0.81/2.0 = 0.405 J I now have a value for Friction force (f) and I then used the relationship Friction = Coefficient of Friction x Normal force .. in this case 0.405=coefficient x mg (Normal force for 8kg-block = weight of block ie. 'mg') So we have coefficient = w/mg = 0.405/(8x9.8) = 0.405/78.8 = 0.02 . However the answer at the back of the book gives coefficient = 0.786. I have tried doing this in slightly different ways and the nearest I get to the correct answer is .. 0.75 (which if you notice is just the mass-ratio between the 2 blocks) ??? So where have I gone wrong ? can anyone help ?