1. The problem statement, all variables and given/known data Hi there, I am a beginner in acoustics and there are severals problems I am currently struggling while I was reading the first chapter of "Theory of Vortex Sound" (available on Google books). 2. Relevant equations For Q4: 3. The attempt at a solution For Q2 and 3, as underlined in the first picture, if the velocity and pressure doesn't go like 1/r , the integral will diverge as r-> inf. However, there are no 1/r terms in U0cos(wt) For Q4, I am not sure how to proceed, since the variable y is contained in two terms within the dirac delta,I don't know how to eliminate it. BTW, I googled sth that might be helpful for Q4. (From P.115-116 of https://books.google.co.uk/books?id...WAhVKDxoKHe_nDiQQ6AEIMjAC#v=onepage&q&f=false ) Thanks very much!!