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# f5ch18 - 498 CHAPTER 18 WAVESII CHAPTER 18 Answer to...

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498 CHAPTER 18 WAVES—II C HAPTER 18 Answer to Checkpoint Questions . beginning to decrease (example: mentally move the curves of Fig. - rightward past the point at x = m) . ( a ) fully constructive, ; ( b ) fully constructive, . ( a ) and tie, then ; ( b ) , then and tie . second . loosen . ( a ) greater; ( b ) less; ( c ) can't tell; ( d ) can't tell; ( e ) greater; ( f ) less . ( a ) m/s; ( b ) m/s Answer to Questions . pulse along path . ( a ) same as rst wave; ( b ) ; ( c ) s m ; ( d ) rad . ( a ) : wavelengths; ( b ) : wavelengths; ( c ) fully constructive, fully destructive . = . ( a ) exactly out of phase; ( b ) exactly out of phase . ( a ) exactly out of phase; ( b ) same . dB . ( a ) one; ( b ) nine . ( a ) two; ( b ) antinode . ( a ) increase; ( b ) decrease . all odd harmonics . d, fundamental

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CHAPTER 18 WAVES—II 499 . , , and Hz; or , , and Hz . ( a ) , then and tie; ( b ) , then and tie; ( c ) , , E ( a ) The speed of sound at C is v s = m/s = ( m/s)( mi = m) = : mi/s ' : mi/s : Thus the distance is D = vt ' ( : mi/s) t = ( t= ) mi ; where t is in seconds. The percent error in D is D D = v v = : mi/s : mi/s : mi/s ' % : ( b ) Similarly, since v s = ( m/s) ' ( = ) km/s, D = vt ' ( t= ) km : So you just need to divide the count by three in stead of ve to obtain the distance in km. E The time it takes for a soldier in the rear end of the colume to switch from the left to the right foot to stride forward is t = min = = = min = : s. This is also the time for the sound of the music to reach from the musicians (who are in the front) to the rear end of the column. Thus the length of the column is l = vt = ( m/s)( : s) = : m : E The time t it takes for you to hear the music is t = D =v s = ( m) = ( m/s) = : s : The time t it takes for a listener km away to hear the music is t = D =c = km = ( km/s) = : s : So the listener km away actually hears the music rst! The time di erence is t = t t = : s : s = : s : E ( a ) The time for the sound to travel from the kicker to a spectator is given by d=v , where d is the distance and v is the speed of sound. The time for light to travel the same distance is given by d=c , where c is the speed of light. The delay between seeing and hearing the kick is t = ( d=v ) ( d=c ). The speed of light is so much greater than the speed of sound that the delay can be approximated by t = d=v . This means d = v t . The distance from the kicker to the rst spectator is d = v t = ( m/s)( : s) = m. The distance from the kicker to the second spectator is d = v t = ( m/s)( : s) = m.
500 CHAPTER 18 WAVES—II ( b ) Lines from the kicker to each spectator and from one spectator to the other form a right triangle with the line joining the spectators as the hypotenuse, so the distance between the spectators is d = p d + d = p ( m) + ( m) = m. E

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f5ch18 - 498 CHAPTER 18 WAVESII CHAPTER 18 Answer to...

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