document.write( "Question 81550: Science and medicine. The equation h= -16t^2 + 112t gives the height of an
\n" ); document.write( "arrow, shot upward from the ground with an initial velocity of 112 ft/s, where t is the time after the arrow leaves the ground. Find the time it takes for the arrow to reach a height of 180 ft. \n" ); document.write( "
Algebra.Com's Answer #58478 by ankor@dixie-net.com(22740)\"\" \"About 
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The equation h=-16t^2 + 112t gives the height of an arrow, shot upward from the ground with an initial velocity of 112 ft/s, where t is the time after the arrow leaves the ground. Find the time it takes for the arrow to reach a height of 180 ft.
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\n" ); document.write( "Substitute 180 for h in the given equation: -16t^2 + 112t = h
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\n" ); document.write( "-16t^2 + 112t = 180
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\n" ); document.write( "-16t^2 + 112t - 180 = 0; subtract 180 from both sides, gives us a quadratic eq:
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\n" ); document.write( "Simplify divide equation by -4, that changes the signs and gives you:
\n" ); document.write( "4t^2 - 28t + 45 = 0
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\n" ); document.write( "Factor this to:
\n" ); document.write( "(2t - 5)(2t - 9) = 0
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\n" ); document.write( "2t = +5
\n" ); document.write( "t = 2.5 sec (on the way up)
\n" ); document.write( "and
\n" ); document.write( "2t = +9
\n" ); document.write( "t = 4.5 sec (on the way down)
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\n" ); document.write( "Check solution using t = 2.5, in the original equation:
\n" ); document.write( "-16(2.5^2) + 112(2.5) =
\n" ); document.write( "-16(6.25) + 280 =
\n" ); document.write( "-100 + 280 = 180
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\n" ); document.write( "You can check it using the t = 4.5 solution \n" ); document.write( "
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