I have been mulling over this question for ages and I just don't know where to start! Question: Two blocks with different mass are attached to either end of a light rope that passes over a light, frictionless pulley that is suspended from the ceiling. The masses are released from rest, and the more massive one starts to descend. After this block has descended a distance s, its speed is v. If the total mass of the two blocks is M, what is the mass of the more massive block? Take free fall acceleration to be g I started off using conservation of potential energy and kinetic energy to try and relate the masses to get that and choosing the height from where the mass fell to be the relative 0- for the larger mass: mgs = 1/2mv^2 but then I realised that I couldn't relate that to the other mass so then i decided to use the equations of motion to find how long the mass took to fall the distance of s getting sqrt(2*s*g) = t Now I am stumped as to what to do - or I could be completely off track - can someone help me out please?