Power of Sound Wave at distance

[Mnemonic]

Homework Statement

A sound source is placed at the top of a (h = 121.5m) radio tower. The source has a frequency of 653.8 Hz and an amplitude of 11.4 nm at point A. The air surrounding the tower has a density of 1.32 kgm-3 and sound travels through it with a velocity of 340 ms-1. Point A is 10.8 m above the source. You may ignore any reflections of the sound from the ground.

Homework Equations

P = (1/2) ρAv (ω s( max ) )^2

The Attempt at a Solution

Determine angular velocity from frequency. Sub in density and velocity.
I think A means amplitude and I would put in 11.3nm.
However, s(max) is "displacement amplitude". Does this mean that s(max) = 11.4nm and A= distance from Point A to sound source?

 

[Mnemonic]

Have been doing some research. A seems to refer to area of the wave sound. So would I be correct in putting A as 4 Pi r squared? Assuming sound is moving out as a sphere?

 

[Mnemonic]

This is indeed the correct method for anyone else who has trouble with this question.