1. The problem statement, all variables and given/known data ) The pulley system in Figure 1.b consists of two pulleys of radii a and b rigidly fixed together, but free to rotate about a common horizontal axis. The weight W hangs from the axle of a freely suspended pulley P, which can rotate about its axle. If section A of a rough rope is pulled down with velocity V : (i) Explain which way W will move. (ii) With what speed will it move? THE IMAGE IS IN QUESTION 3 HERE: http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_Round_1_2013_prt_1.pdf 2. Relevant equations - 3. The attempt at a solution The answer is that the weight will move up because rope B moves down with velocity (b/a)V and D moves up with velocity V, so the centre of the weight rises with speed V(a-b)/2a I really can't see why the mass would move up. Surely the same amount of string is fed through to each side of the pulley so it should not move? Thank you in advance!