document.write( "Question 1139838: In an experiment, a ball is released from a building. If the height of the ball after released is given by the equation h= -4.9t2+19.6t=686, where h is the height of the ball and t is the elapsed time after it is released, after how many seconds will the ball hit the ground? \n" ); document.write( "

Algebra.Com's Answer #760325 by ikleyn(52781) $\"\"$ $\"About$

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\n" ); document.write( "\n" ); document.write( " Your equation is written INCORRECTLY.\r
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\n" ); document.write( "\n" ); document.write( " The correct form is h(t) = -4.9t^2 + 19.6t + 686 , where h is measured in feet.\r
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document.write( "The ball will hit the ground, when  h(t) = 0,  or, equivalently,\r\n" );
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document.write( "    -4.9t^2 + 19.6t + 686 = 0.\r\n" );
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document.write( "Simplify by dividing by (-4.9) to get\r\n" );
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document.write( "    t^2 - 4t - 140 = 0,\r\n" );
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document.write( "    (t-14)*(t+10) = 0.\r\n" );
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document.write( "Of the two roots,  t= 14  and  t= -10,  only positive t = 14 is meaningful, giving the\r\n" );
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document.write( "ANSWER.  t= 10 seconds.\r\n" );
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