Three pieces of string, each of length l, are joined together end to end, to make a combined string of length 3 l. the first piece of string has mass per unit length μ1, the second piece has mass per unit length μ2=4μ1, and the third piece has mass per unit length μ3=μ1/4. (a) if the combined string is under tension f, how much time does it take a transverse wave to travel the entire length 3l? give your answer in terms of l, f, and μ1. (b) does your answer to part (a) depend on the order in which the three pieces are joined together? explain.