document.write( "Question 75081: A ball is thrown upward from the roof of a building 100 m tall with an initial velocity of 20 m/s.\r
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Algebra.Com's Answer #53941 by Edwin McCravy(20055)\"\" \"About 
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document.write( "A ball is thrown upward from the roof of a \r\n" );
document.write( "building 100 m tall with an initial velocity\r\n" );
document.write( "of 20 m/s. When will the ball reach a height\r\n" );
document.write( "of 80 m?  Please show work.\r\n" );
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document.write( "The formula is\r\n" );
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document.write( "                h = hO + vOt - 4.9t²\r\n" );
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document.write( "where\r\n" );
document.write( "h = final height in m, which here is 80m\r\n" );
document.write( "hO = initial height in m, which here is 100m\r\n" );
document.write( "vO = initial velocity in m/s, which here is +20m/s\r\n" );
document.write( "     (+ because it's upward)\r\n" );
document.write( "t = final time in s, which is what we need to find.\r\n" );
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document.write( "                h = hO + vOt - 4.9t²\r\n" );
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document.write( "               80 = 100 + 20t - 4.9t²\r\n" );
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document.write( " 4.9t² - 20t + 80 = 100\r\n" );
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document.write( " 4.9t² - 20t - 20 = 0\r\n" );
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document.write( "49t² - 200t - 200 = 0\r\n" );
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document.write( "Use the quadratic formula:\r\n" );
document.write( "                  ______ \r\n" );
document.write( "            -b ± Öb²-4ac\r\n" );
document.write( "        x = —————————————\r\n" );
document.write( "                2a \r\n" );
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document.write( "where a = 49; b = -200; c = -200\r\n" );
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document.write( "                        ___________________ \r\n" );
document.write( "             -(-200) ± Ö(-200)²-4(49)(-200)\r\n" );
document.write( "        x = ————————————————————————————————\r\n" );
document.write( "                       2(49) \r\n" );
document.write( "                    ___________ \r\n" );
document.write( "             200 ± Ö40000+39200\r\n" );
document.write( "        x = ————————————————————\r\n" );
document.write( "                     98\r\n" );
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document.write( "                    _____ \r\n" );
document.write( "             200 ± Ö79200\r\n" );
document.write( "        x = ——————————————\r\n" );
document.write( "                   98\r\n" );
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document.write( "                    _______ \r\n" );
document.write( "             200 ± Ö3600·22\r\n" );
document.write( "        x = ———-—————————————\r\n" );
document.write( "                   98 \r\n" );
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document.write( "                      __\r\n" );
document.write( "             200 ± 60Ö22\r\n" );
document.write( "        x = —————————————\r\n" );
document.write( "                  98\r\n" );
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document.write( "                       __\r\n" );
document.write( "             20(10 ± 3Ö22)\r\n" );
document.write( "        x = ———————————————\r\n" );
document.write( "                  98\r\n" );
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document.write( "             10        __       \r\n" );
document.write( "             20(10 ± 3Ö22)\r\n" );
document.write( "        x = ———————————————\r\n" );
document.write( "                  98\r\n" );
document.write( "                  49\r\n" );
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document.write( "                       __\r\n" );
document.write( "             10(10 ± 3Ö22)\r\n" );
document.write( "        x = ———————————————\r\n" );
document.write( "                  49\r\n" );
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document.write( "Using the +\r\n" );
document.write( "                       __\r\n" );
document.write( "             10(10 + 3Ö22)\r\n" );
document.write( "        x = ———————————————\r\n" );
document.write( "                  49      \r\n" );
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document.write( "        x = 4.912399445\r\n" );
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document.write( "Using the -\r\n" );
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document.write( "             10(10 - 3Ö22)\r\n" );
document.write( "        x = ———————————————\r\n" );
document.write( "                  49      \r\n" );
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document.write( "        x = -0.8308667917\r\n" );
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document.write( "which we discard since we can't have negative time.\r\n" );
document.write( "So the answer rounded to the nearest tenth is\r\n" );
document.write( "4.9 seconds. \r\n" );
document.write( "                 \r\n" );
document.write( "Edwin

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