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Unformatted text preview: cerutti (cpc566) HW12 TSOI (58160) 1 This printout should have 22 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Radio waves travel at the speed of light: 3 10 5 km / s. What is the wavelength of radio waves re ceived at 97 . 9 MHz on your FM radio dial? Correct answer: 3 . 06435 m. Explanation: Let : v = 3 10 5 km / s = 300 million m / s and f = 97 . 9 MHz = 97 . 9 million Hz . = v f = 300 million m / s 97 . 9 million Hz = 3 . 06435 m . 002 10.0 points Earthquakes produce two kinds of seismic waves: he longitudinal primary waves (called P waves) and the transverse secondary waves (called S waves). Both S waves and P waves travel through Earths crust and mantle, but at different speeds; the P waves are always faster than the S waves, but their exact speeds depend on depth and location. For the pur pose of this exercise, we assume the P waves speed to be 9990 m / s while the S waves travel at a slower speed of 5980 m / s. If a seismic station detects a P wave and then 21 . 1 s later detects an S wave, how far away is the earthquake center? Correct answer: 314 . 344 km. Explanation: Let : v P = 9990 m / s , v S = 5980 m / s , and t = 21 . 1 s . Suppose the earthquake happens at time t = 0 at some distance d . The P wave and the S wave are both emitted at the same time t = 0, but they arrive at different times, re spectively t P = d v P and t S = d v S . The S wave is slower, so it arrives later than the P wave, the time difference being t = d v S d v P = d ( v P v S ) v P v S . Consequently, given this time difference and the two waves speeds v P and v S , the earth quake center is d = v P v S t v P v S = (9990 m / s) (5980 m / s) (21 . 1 s) 9990 m / s 5980 m / s 1 km 1000 m = 314 . 344 km away from the seismic station. 003 (part 1 of 2) 10.0 points A wave moving along the x axis is described by y ( x,t ) = Ae ( x + v t ) 2 /b where x is in meters, t is in seconds, A = 4 m, v = 5 m / s, and b = 4 m 2 . Determine the speed of the wave. Correct answer: 5 m / s. Explanation: y ( x,t ) = Ae ( x + v t ) 2 /b is of the form y ( x,t ) = f ( x + v t ) so it describes a wave at v = 5 m / s . 004 (part 2 of 2) 10.0 points Determine the direction of the wave. 1. x direction correct 2. + x direction 3. y direction cerutti (cpc566) HW12 TSOI (58160) 2 4. + y direction Explanation: f ( x + v t ) = f ( x ( v ) t ) so the wave is moving at 5 m / s (in the negative direction). 005 (part 1 of 2) 10.0 points The time interval indicated on this diagram is G . + S S S t (seconds) G Which formula corresponds best to the di agram?...
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 Spring '08
 Turner
 Physics, Light

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