# Homework Help: Mechanical waves - average power transmitted

1. Jul 30, 2009

### Str1k3

1. The problem statement, all variables and given/known data
show, using the propagating wave y = Ae^[i(wt - kx)] that the average power transmitted across any point on the string in a complete full cycle is given by P = vE (P and E are both vectors). v is the phase velocity and E the total average energy density per cycle. also show that div(P) + dE/dt = 0 for the wave. Here E is the total energy density and P is the directed instantaneous power transmitted across a point.

2. Relevant equations
in the question statement

3. The attempt at a solution
i don't even know where to begin! i have run out of internet cap (this is my last little bit of data for the month) and i don't have a text book - and there are none left in the library. my lecturer's notes are quite useless too, as they don't explain anything i need for this question. if anyone could help me i would really appreciate it, i'm totally lost!