Why are metals good conductors of electric current? choose one of the followingdo they possess high concentrations of protonsdo they possess low concentrations of protonsdo they possess high concentrations of free electronsdo they possess low concentrations of free electrons

Consider a double atwood machine constructed as follows: a mass 4m is suspended from a string that passes over a massless pulley on frictionless bearings. the other end of this string supports a second similar pulley, over which passes a second string supporting a mass of 3m at one end and m at the other. using two suitable generalized coordinates, set up the lagrangian and use the lagrange equations to find the acceleration of the mass 4m when the system is released. explain why the top pulley rotates even though it carries equal weights on each side.