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Unformatted text preview: Create assignment, 00224, Homework 2, Jan 24 at 10:21 am 1 This printout should have 10 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. The due time is Central time. Hikers Hear an Echo 17:02, trigonometry, numeric, > 1 min, nor mal. 001 A group of hikers hear an echo 3 s after they shout. The temperature is 22 C. How far away is the mountain that reflected the sound wave? At this altitude, the speed of sound in air at 273 C is 329 m / s. Correct answer: 512 . 999 m. Explanation: Let : t = 3 s , T = 22 C , T = 273 C , and v = 329 m / s . The velocity at 22 C is v = v r 1 + T T v = (329 m / s) r 1 + 22 C 273 C = 342 m / s . If d is the distance to the object, the total distance traveled by the sound (there and back) is 2 d. Thus, 2 d = v t d = v t 2 = (342 m / s) (3 s) 2 = 512 . 999 m . keywords: Serway CP 14 20 17:05, trigonometry, numeric, < 1 min, nor mal. 002 A train at rest emits a sound at a frequency of 1000 Hz. An observer in a car travels away from the sound source at a speed of 30 m / s. What is the frequency heard by the ob server? Assume the speed of sound in air to be 343 m / s. Correct answer: 912 . 536 Hz. Explanation: Given : f = 1000 Hz , v = 30 m / s , and v = 343 m / s . f = f v v v v s = f v v v since the source is stationary and the observer is moving away from the source. Then f = (1000 Hz) 343 m / s 30 m / s 343 m / s = 912 . 536 Hz ....
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 Spring '10
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