1. The problem statement, all variables and given/known data B, K, M 2. Relevant equations 1. xs(t) -----spring ----mass-----damper-----fixed, derive DE for x of mass given :2. F - > M -----spring-------damper ---- fixed in series, derive the DE for velocity of spring 3. The attempt at a solution 1. ma = -k(x-xs) - B(v) But I don't understand, why aren't we taking the natural length of the spring into account? 2. no idea, I have the solution and it says that damping force is B(v(t) - vk) , but I have no idea what v has anything to do with damper, the relative velocity vb should just be vk - 0 to me but the textbook and the hw solution suggest otherwise.