1. The problem statement, all variables and given/known data a light, inextensible string passes over a small pulley and carries a mass of 2m on one end. on the other end is a mass m, and beneath it, supported by a spring w/ spring constant k, is a second mass m. using the distance x, of the first mass beneath the pulley, and the extension y in the spring, as generalized co-ordinates, find the hamiltonian 2. Relevant equations H=kinetic energy+potential 3. The attempt at a solution The problem, as stated above, is copied straight from the book, and I am not really sure what the coordinate x describes. ill call the mass of 2m "M1" & "M2" is the mass connected to the string from above, and spring from below & "M3" is the mass hanging from the spring. In my setup, x is the distance from the pully to M1, and y is the extension of the spring so the kinetic energy in terms of x and y: for M1: KE= m(dx/dt)^2 M2: KE= 1/2 m(dx/dt)^2 M3: KE=1/2 m(dy/dt+dx/dt)^2 Then for the system, KE =3/2 m(dx/dt)^2+1/2 m(dy/dt+dx/dt)^2 I am struggling writing down the potential in terms of x and y M1 will have only that of gravity, where as the other 2 will also have a spring term. Can anybody point me in the right direction with these coordinates?