hw39 - homework 39 Turner (58185) This print-out should...

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This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points A ±owerpot is knocked o² a balcony 25 . 5 m above the sidewalk and Falls toward an un- suspecting 1 . 64 m tall man who is standing below. How close to the side walk can the ±ower pot Fall beFore it is too late For a warning shouted From the balcony to reach the man in time? Assume that the man below requires 0 . 249 s to respond to the warning, and the velocity oF sound in air to be 344 m / s. The acceleration oF gravity is 9 . 8 m / s 2 . Correct answer: 8 . 02803 m. Explanation: Let : v s = 344 m / s , H = 25 . 5 m , h m = 1 . 64 m , and t r = 0 . 249 s . h 2 = gt 2 2 /2 t 2 = t - t 1 h = H - h m t = (2 h / g ) 1/2 h 1 = h - h 2 t 1 = t r + t s h m h m H H 1 The distance From the balcony to the man’s head is h = H h m , The time For a warning to travel this dis- tance is t s = h v s = H h m v s . The total time needed to receive the warn- ing and react is t 1 = t s + t r = H h m v s + t r , and the time For the pot to Fall this distance (starting From rest) is t = r 2 h g = r 2 ( H h m ) g . Thus the latest the warning can be sent is at t 2 = t t 1 = r 2 ( H h m ) g H h m v s t r = r 2 (25 . 5 m 1 . 64 m) 9 . 8 m / s 2 25 . 5 m 1 . 64 m 344 m / s 0 . 249 s = 1 . 88831 s into the Fall. In this time the pot has Fallen a distance oF h 2 = 1 2 g t 2 2 and the corresponding height above the side- walk is H 1 = H h 2 = H 1 2 g t 2 2 = 25 . 5 m 1 2 ( 9 . 8 m / s 2 ) (1 . 88831 s) 2 = 8 . 02803 m . 002 10.0 points Sound waves travel through a liquid oF density 9240 kg / m 3 at a speed oF 4440 m / s. What is the bulk modulus oF this liquid? Correct answer: 1 . 82154 × 10 11 Pa. Explanation: Let : ρ = 9240 kg / m 3 and v sound = 4440 m / s . homework 39 – Turner – (58185) 1
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hinojosa (jlh3938) – homework 39 – Turner – (58185) 2 In fuids, sound waves are pressure waves, and their speed depends on the fuid’s density and bulk modulus: v sound = r B ρ . For the liquid in question, we know the density and the speed o± sound, so the bulk modulus is B = ρ v 2 sound = (9240 kg / m 3 ) (4440 m / s) 2 = 1 . 82154 × 10 11 Pa . 003 10.0 points A harmonic wave y = A sin[ k x ω t φ ] , where A = 1 m, k has units o± m 1 , ω has units o± s 1 , and φ has units o± radians, is plotted in the diagram below.
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This note was uploaded on 05/02/2009 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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hw39 - homework 39 Turner (58185) This print-out should...

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