Two boys weighing 60 N and 70 N sit on a see-saw. The boy weighing 60 N sits on the left side of a seesaw at a distance of 1m from the pivot while the other boy sits on the right side at a distance of 1.2 m. What distance must a third boy of weight 80 N sit on the left side in order to balance the see-saw?

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.