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Unformatted text preview: sanchez (ds28677) – homework 34 – Turner – (58220) 1 This printout should have 13 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A flowerpot is knocked off a balcony 30 . 4 m above the sidewalk and falls toward an un suspecting 1 . 86 m tall man who is standing below. How close to the side walk can the flower 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 . 477 s to respond to the warning, and the velocity of sound in air to be 345 m / s. The acceleration of gravity is 9 . 8 m / s 2 . Correct answer: 13 . 5631 m. Explanation: Let : v s = 345 m / s , H = 30 . 4 m , h m = 1 . 86 m , and t r = 0 . 477 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 and 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 = radicalBigg 2 h g = radicalBigg 2 ( H − h m ) g . Thus the latest the warning can be sent is at t 2 = t − t 1 = radicalBigg 2 ( H − h m ) g − H − h m v s − t r = radicalBigg 2 (30 . 4 m − 1 . 86 m) 9 . 8 m / s 2 − 30 . 4 m − 1 . 86 m 345 m / s − . 477 s = 1 . 85367 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 = 30 . 4 m − 1 2 ( 9 . 8 m / s 2 ) (1 . 85367 s) 2 = 13 . 5631 m . 002 10.0 points Sound waves travel through a liquid of density 7080 kg / m 3 at a speed of 5400 m / s. What is the bulk modulus of this liquid? Correct answer: 2 . 06453 × 10 11 Pa. Explanation: sanchez (ds28677) – homework 34 – Turner – (58220) 2 Let : ρ = 7080 kg / m 3 and v sound = 5400 m / s . In fluids, sound waves are pressure waves, and their speed depends on the fluid’s density and bulk modulus: v sound = radicalBigg B ρ B = ρ v 2 sound = (7080 kg / m 3 ) (5400 m / s) 2 = 2 . 06453 × 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 of m − 1 , ω has units of s − 1 , and φ has units of radians, is plotted in the diagram below....
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 Spring '08
 Turner
 Physics, Work, Correct Answer, Sanchez

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