Consider a see-saw where one side is twice the length of the other side. A child with mass 36 kg sits on the longer end, and their parent sits on the shorter end, both experiencing a force due to gravity. What should the mass of the parent be in order for the see-saw to be perfectly balanced when (a) the see-saw is approximately massless, and when (b) the see-saw has mass 15 kg. If you are stuck on this one, at least be able to explain why the answer is different from part a.