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**Unformatted text preview: **Overton, Mays – Homework 34 – Due: Apr 29 2005, 4:00 am – Inst: Turner 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points Given: At this altitude, the speed of sound in air at 273 ◦ C is 332 m / s. A group of hikers hear an echo 3 . 9 s after they shout. The temperature is 23 ◦ C. How far away is the mountain that reflected the sound wave? Correct answer: 674 . 12 m. Explanation: v = (332 m / s) s 1 + (23 ◦ C) (273 ◦ C) = 345 . 703 m / s . If d is the distance to the object, the total distance traveled by the sound (there and back) is 2 d . Thus, d = v • t 2 ‚ = (345 . 703 m / s) • (3 . 9 s) 2 ‚ = 674 . 12 m . 002 (part 1 of 1) 10 points Given: The speed of the lightwaves in air is 3 × 10 8 m / s. The speed of sound waves in air is 333 m / s. What is the time lapse between seeing a lightening strike and hearing the thunder if the lightening flash is 30 km away? Correct answer: 90 . 09 s. Explanation: The time for the light to travel 30 km is t 1 = d v 1 . The time for the sound to travel 30 km is t 2 = d v 2 . Thus, the time lapse is Δ t = t 2- t 1 = d µ 1 v 2- 1 v 1 ¶ = (30 km) × µ 1 333 m / s- 1 3 × 10 8 m / s ¶ = 90 . 09 s . 003 (part 1 of 1) 10 points Carol drops a stone into a mine shaft 143 . 7 m deep. Take the speed of sound as 343 m / s. The acceleration of gravity is 9 . 8 m / s 2 . How soon after she drops the stone does she hear it hit the bottom of the shaft? Correct answer: 5 . 83435 s. Explanation: The speed of sound in air at room temper- ature is v s = 343 m / s. Two times are involved: 1) The stone travels to the bottom via free fall: d = 1 2 g t 2 1 , so that t 1 = s 2 d g 2) The sound travels back to the top of the shaft: t 2 = d v s ....

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