document.write( "Question 1142011: 12. The nearby beach has an average depth of the water at low tide of 1 m at midnight. The average depth of the water at high tide is 8 m at 6am. One complete cycle takes 12 h.
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\n" ); document.write( "(b) Many people dive from this pier during the day. If the water must be at least 3 m deep to dive safely, between what daylight hours should people dive?
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Algebra.Com's Answer #762677 by ikleyn(52810) $\"\"$ $\"About$

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document.write( "The formula for the 12-hours cycle is  \r\n" );
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document.write( "    y = , \r\n" );
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document.write( "where x is the measure of the time in hours, starting from x= 0 at midnight and till x= 12 hours (the noon), \r\n" );
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document.write( "which is about one full tide cycle.\r\n" );
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document.write( "Check.  At x = 0 hours (midnight)  y =  = -3.5*1 + 4.5 = - 3.5 + 4.5 = 1 meter  (lowest tide level);\r\n" );
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document.write( "        at x= 3 hours  y =  =  =  =  = 4.5 meters;\r\n" );
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document.write( "        at x = 6 hours  y =  =  =  =  = 8 meters  (highest tide level);\r\n" );
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document.write( "        at x = 9 hours  y =  =  =  = 4.5 meters;\r\n" );
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document.write( "        at x = 12 hours  (at noon)  y =  =  = -3.5*1+ 4.5) = -3.5 + 4.5 = 1 meter  (lowest tide level, again).\r\n" );
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document.write( "The period (one full cycle) is equal to  12 hours:   = , as it should be.\r\n" );
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\n" ); document.write( "\n" ); document.write( "You can use the same formula for the two consecutive full tide cycles (of the total 24 hours duration), too.\r
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\n" ); document.write( "\n" ); document.write( "To get familiar with the subject, read this Internet article\r
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\n" ); document.write( "\n" ); document.write( "https://oceanservice.noaa.gov/education/tutorial_tides/tides05_lunarday.html\r
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document.write( "    Because the Earth rotates through two tidal “bulges” every lunar day, coastal areas experience two high and two low tides \r\n" );
document.write( "    every 24 hours and 50 minutes. High tides occur 12 hours and 25 minutes apart. It takes six hours and 12.5 minutes \r\n" );
document.write( "    for the water at the shore to go from high to low, or from low to high.\r\n" );
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