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Elastic Waves. Acoustics.

Problem 4.186

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

Reveal Answer
⟨Φ⟩=πR2(Δp)m2/2ρvλ=11 mW\langle\Phi\rangle=\pi R^{2}(\Delta p)_{m}^{2} / 2 \rho v \lambda=11 \mathrm{~mW}
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