I'm revising for my exam and there's this one problem where I can't get the correct answer, so I'd like to know how to solve it. The problem is:
Two boys, each with a mass of 30kg, are sitting on the ends of a horizontal girder which is 2.5m long and has a mass of 15 kg. The girder rotates at 7 turns/minute around a vertical axis through its center.
a) What is the angular speed if each boy moves forward 29 cm?
b) What is the change in kinetic energy?
(I added the homework tag, but it's not like I have to solve this, I just don't know how to.)