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HW 16 - johnson(mjj622 HW 16 Coker(56625 This print-out...

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johnson (mjj622) – HW 16 – Coker – (56625) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. This assignment covers the material dis- cussing sound waves as presented in class, including longitudinal pressure waves, sound intensity, loudness, the Doppler e±ect, and standing sound waves. 001 10.0 points Sound with a Frequency oF 430 Hz travels through steel. A wavelength oF 14 . 46 m is measured. What is the speed oF the sound in steel? Correct answer: 6217 . 8 m / s. Explanation: Let : f = 430 Hz and λ = 14 . 46 m . v = f λ = (430 Hz) (14 . 46 m) = 6217 . 8 m / s . 002 10.0 points Calculate the pressure amplitude oF a 1 . 36 kHz sound wave in air iF the displace- ment amplitude is 2 . 35 × 10 8 m. Take the velocity oF sound in air to be 343 m / s and the density oF air to be 1 . 31 kg / m 3 . Correct answer: 0 . 0902302 Pa. Explanation: Let : f = 1 . 36 kHz = 1360 Hz , A = 2 . 35 × 10 8 m , v s = 343 m / s , and ρ = 1 . 31 kg / m 3 . The pressure amplitude is Δ P = ρ ω v s A = ρ (2 π f ) v s A = (1 . 31 kg / m 3 ) 2 π (1360 Hz) × (343 m / s) (2 . 35 × 10 8 m) = 0 . 0902302 Pa . 003 (part 1 of 2) 10.0 points A sinusoidal sound wave in a gas oF density 1 . 3 kg 3 / m has molecular displacement s ( x, t ) = s m cos( k x ω t ) , where s m = 4 μ m, k = 728 m 1 , and ω = 4 . 4408 × 10 5 s 1 . What is the speed oF this wave? Correct answer: 610 m / s. Explanation: Let : k = 728 m 1 and ω = 4 . 4408 × 10 5 s 1 . The speed oF the wave is v = ω k = 4 . 4408 × 10 5 s 1 728 m 1 = 610 m / s . 004 (part 2 of 2) 10.0 points What is the intensity oF this wave? Correct answer: 1251 . 08 W / m 2 . Explanation: Let : ρ = 1 . 3 kg 3 / m and s m = 4 μ m = 4 × 10 6 m . I = 1 2 ρ v ( ω s m ) 2 = 1 2 (1 . 3 kg 3 / m) (610 m / s) × (4 . 4408 × 10 5 s 1 ) 2 × (4 × 10 6 m) 2 = 1251 . 08 W / m 2 . 005 (part 1 of 2) 10.0 points The area oF a typical eardrum is about 4 . 9 × 10 5 m 2 .

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johnson (mjj622) – HW 16 – Coker – (56625) 2 Find the sound power (the energy per sec- ond) incident on an eardrum at the threshold of hearing ( 1 × 10 12 W / m 2 ) . Correct answer: 4
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HW 16 - johnson(mjj622 HW 16 Coker(56625 This print-out...

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