Aside from a permanent magnet a magnetic field can also generated directly by which of the following? Help-

An object has a weight of 500 on earth what is the mass of this object

What will a positive and a negative charge do if they are separated from each other?

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.