How are electric potential difference and electric potential energy related? Electric potential difference is the charge divided by the difference in electric potential energy. Electric potential energy is the charge divided by the electric potential difference. Electric potential difference is the difference in electric potential energy divided by the charge. Electric potential energy is the electric potential difference divided by the charge.

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.