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Unformatted text preview: yang (ey942) – HW13 – TSOI – (58160) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Sound in air can best be described as which of the following type of wave? 1. Longitudinal correct 2. Electromagnetic 3. Polarized 4. Torsional 5. Transverse Explanation: A sound wave in the air is propagated by the oscillation of air molecules. It is best described as longitudinal wave. 002 10.0 points Middle C has a speed of 1500 m/s in water and 340 m/s in air. Does it have a longer or shorter wavelength in water than in air and why? 1. Longer; water is denser than air. 2. Longer; the speed of sound is greater in water than in air. correct 3. Shorter; water is denser than air. 4. Shorter; the speed of sound is greater in water than in air. Explanation: wavelength = velocity frequency The velocity of sound in water is larger than in air. The frequency doesn’t change, so the wavelength in water is larger than in air. 003 10.0 points An oceanic depth-sounding vessel surveys the ocean bottom with ultrasonic waves that travel 1530 m / s in seawater. How deep is the water directly below the vessel if the time delay of the echo to the ocean floor and back is 4 s? Correct answer: 3060 m. Explanation: Let : v = 1530 m / s and Δ t = 4 s . The sound takes 2 s to reach the ocean floor (and 2 s to return), so d = v t = (1530 m / s) (2 s) = 3060 m . 004 10.0 points What two physics mistakes occur in a science fiction movie that shows a distant explosion in outer space, where you see and hear the explosion at the same time? 1. None of these 2. In outer space there is no material to carry light; if there were, the sound would reach you before the light. 3. The explosion cannot occur in outer space; if it could, the sound would reach you before the light. 4. The explosion cannot occur in outer space; if it could, the faster-moving light would reach you before the sound. 5. In outer space there is no air to carry sound; if there were, the faster-moving light would reach you before the sound. correct Explanation: First, in outer space there is no air or other material to carry sound, so you can- not hear the sound. Second, if there were, faster-moving light would reach you before the sound. 005 10.0 points yang (ey942) – HW13 – TSOI – (58160) 2 What beat frequencies are possible with tun- ing forks of frequencies 256, 259, and 261 Hz? 1. 3 possible: 515 Hz, 520 Hz, and 517 Hz. 2. 2 possible: 2 Hz and 3 Hz. 3. 4 possible: 2 Hz, 3 Hz, 5 Hz, and 7 Hz. 4. 3 possible: 2 Hz, 3 Hz, and 5 Hz. correct 5. 3 possible: 256 Hz, 259 Hz, and 261 Hz. Explanation: The beat frequencies are the differences in the fork frequencies: 261 Hz- 259 Hz = 2 Hz , 261 Hz- 256 Hz = 5 Hz , 259 Hz- 256 Hz = 3 Hz ....
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- Fall '10
- Decibel, Correct Answer