1. The problem statement, all variables and given/known data Please look at this pdf http://iweb.tntech.edu/murdock/books/v1chap4.pdf PDF pg. 18 - 22 Question# 14 2. Relevant equations Fnet = ma v = d/t d^2 x / dt^2 = a and so on 3. The attempt at a solution I don't understand the solution he gives. Please turn to PDF page 20 The author says (first paragraph) Now I don't understand how sure we know it is x. Why can't it be X + 2, or X + 1500?? Later he says total length of the string is L, so it assumes that the entire system is actually running with one single string?? The given did not say that, and the diagram did not show that either. In solving this problem, what do we have to think first? it seems very insightful that one sees the relationship in distance.