This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: homework 36 VALENCIA, DANIEL Due: Apr 26 2008, 4:00 am 1 Question 1, chap 17, sect 2. part 1 of 1 10 points An explosive charge is detonated at a height of several kilometers in the atmosphere. At a distance of 609 m from the explosion the acoustic pressure reaches a maximum of 14 . 1 N / m 2 . The density of the air is 1 . 49 kg / m 3 and the speed of sound is 343 m / s and sound waves in air are absorbed at a rate of approximately 4 . 1 dB / km. What will be the sound level at a distance 4 . 08 km from the explosion? Consider the atmosphere to be homogeneous over the dis tances considered. Correct answer: 82 . 1373 dB (tolerance 1 %). Explanation: Let : = 4 . 1 dB / km , L 1 = 609 m , P m = 14 . 1 N / m 2 , = 1 . 49 kg / m 3 , v = 343 m / s , and L 2 = 4 . 08 km . The intensity at L 1 is I 1 = P 2 m 2 v = (14 . 1 N / m 2 ) 2 2 (1 . 49 kg / m 3 ) (343 m / s) = 0 . 194504 W / m 2 . Since the intensity is inversely proportional to the distance squared, I 2 I 1 = L 2 1 L 2 2 I 2 = I 1 L 2 1 L 2 2 = (0 . 194504 W / m 2 ) (609 m) 2 (4 . 08 km) 2 = 0 . 00433353 W / m 2 . The sound level at L 2 is 2 = 10 log parenleftbigg I 2 I parenrightbigg = 10 log parenleftbigg . 00433353 W / m 2 1 10 12 W / m 2 parenrightbigg = 96 . 3684 dB , so allowing for absorption of the wave over the distance traveled, 2 = 2 ( L 2 L 1 ) = 96 . 3684 dB (4 . 1 dB / km) (4 . 08 km . 609 km) = 82 . 1373 dB . Question 2, chap 17, sect 2. part 1 of 1 0 points A rock band plays at a 74 dB sound level. How many times greater is the sound pressure from another rock band playing at 114 dB? Correct answer: 100 (tolerance 1 %). Explanation: Let : 1 = 74 dB and 2 = 114 dB . For a given sound level, every increase of 20 dB corresponds to a pressure amplitude 10 times larger than the original pressure ampli tude, so n = 10 ( 2 1 ) / 20 = 10 (114 dB 74 dB) / (20 dB) = 100 . Question 3, chap 17, sect 2. part 1 of 3 10 points A point source emits sound waves uniformly in all directions with a power output P . r rock concert A homework 36 VALENCIA, DANIEL Due: Apr 26 2008, 4:00 am 2 What is the intensity of the sound waves detected by a receiver a distance r from the source? Assume the receiver has a cross sec tion A perpendicular to the direction of the incident sound....
View Full
Document
 Spring '08
 Turner
 Charge, Work

Click to edit the document details