A ball of radius `R=50 cm` is located in the way of propagation of a plane sound wave. The sonic wavelength is `lambda=20cm`, the frequency is `v= 1700 Hz`, the pressure oscillation amplitude in air is `(Deltap)_(m)=3.5 Pa`. Find the mean energy flow, averaged over an oscillation period, reaching the surface of the ball.

Explanation

The intensity of the sound wave is ltbr. `I=((Deltap)_(m)^(2))/( 2 rho v)=((Deltap)_(m)^(2))/(2 rho v lambda)`
Using `v=vlambda, rho` is the density of air.
Thus the mean energy flow reachind the ball is
`pi R^(2)I=pi R^(2)((Delta)_(m)^(2))/(2 rho v lambda)`
`pi R^(2)` being the effective area `(` area of cross section `)` of the ball.
Substitution gives `10.9 m W`.