document.write( "Question 1204872: Earthquakes produce several types of shock waves. The most well known are the P-waves (P for primary or pressure) and the S-waves (S for secondary or shear). In the earth's crust, P-waves travel at about 6.5 km/s and S-waves move at about 3.5 km/s. The time delay between the arrival of these two waves at a seismic recording station tells geologists how far away an earthquake occurred. If the time delay is 33 seconds, how far from the seismic station did the earthquake occur? \r
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Algebra.Com's Answer #841408 by ikleyn(52797) $\"\"$ $\"About$

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\n" ); document.write( "Earthquakes produce several types of shock waves. The most well known are the P-waves
\n" ); document.write( "(P for primary or pressure) and the S-waves (S for secondary or shear).
\n" ); document.write( "In the earth's crust, P-waves travel at about 6.5 km/s and S-waves move at about 3.5 km/s.
\n" ); document.write( "The time delay between the arrival of these two waves at a seismic recording station
\n" ); document.write( "tells geologists how far away an earthquake occurred. If the time delay is 33 seconds,
\n" ); document.write( "how far from the seismic station did the earthquake occur?
\n" ); document.write( "(problem from Young and Freedman. University Physics with Modern Physics. Fifteenth Edition)
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document.write( "Let d be the distance under the question.\r\n" );
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document.write( "The travel time for P-wave is    seconds  (the distance divided by the speed).\r\n" );
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document.write( "The travel time for S-wave is    seconds  (the distance divided by the speed).\r\n" );
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document.write( "The difference of these travel times is the time delay\r\n" );
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document.write( "     -  = 33 seconds.\r\n" );
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document.write( "It is your basic equation. It is called sometimes \"a time equation\", because both its parts represent the time.\r\n" );
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document.write( "As soon as you got it, the setup is completed.\r\n" );
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document.write( "To solve this equations, multiply both sides by 3.5*6.5.  You will get then\r\n" );
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document.write( "    6.5d - 3.5d = 3.5*6.5*33,\r\n" );
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document.write( "or\r\n" );
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document.write( "        3d      =   750.75.\r\n" );
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document.write( "Hence,  d =  = 250.25.\r\n" );
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document.write( "We can round it to 250 km.\r\n" );
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document.write( "ANSWER.  Earthquack occured 250 km from the seismic station.\r\n" );
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\n" ); document.write( "\n" ); document.write( "Solved.\r
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\n" ); document.write( "\n" ); document.write( "It is one of many applications of \"time equation\" methodology to real life problems.\r
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\n" ); document.write( "\n" ); document.write( "To see other similar (and different) Travel & Distance problems, look into the lesson\r
\n" ); document.write( "\n" ); document.write( " - Earthquacke waves\r
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