document.write( "Question 80324: HELP ASAP!!!! An object is propelled vertically upward from the top of a 112-foot building. The quadratic function s(t) = -16t^2 + 176t + 112 models the ball’s height above the ground, s(t) in feet, t seconds after it was thrown. How many seconds does it take until the object finally hits the ground? Round to the nearest tenth of a second if necessary. \n" ); document.write( "

Algebra.Com's Answer #57639 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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An object is propelled vertically upward from the top of a 112-foot building. The quadratic function s(t) = -16t^2 + 176t + 112 models the ball’s height above the ground, s(t) in feet, t seconds after it was thrown. How many seconds does it take until the object finally hits the ground? Round to the nearest tenth of a second if necessary.
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\n" ); document.write( "When the object hit's the ground the height, s(t) = 0 so we have:
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\n" ); document.write( "-16t^2 + 176t + 112 = 0
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\n" ); document.write( "Fortunately we can simplify things by dividing equation by -16
\n" ); document.write( "t^2 - 11t - 7 = 0
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\n" ); document.write( "Use the quadratic formula: a=1; b=-11; c=-7 (we only care about the positive solution)
\n" ); document.write( " $\"t+=+%28%2B11+%2B-+sqrt%28+121+-4+%2A+1+%2A+-7+%29%29%2F%282%29+\"$
\n" ); document.write( ":
\n" ); document.write( " $\"t+=+%28%2B11+%2B-+sqrt%28149+%29%29%2F%282%29+\"$
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\n" ); document.write( " $\"t+=+%28%2B11+%2B+12.2%29%2F%282%29+\"$
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\n" ); document.write( "t = 11.6 sec
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\n" ); document.write( "Check solution in original equation:
\n" ); document.write( "-16(11.6^2) + 176(11.6) + 112
\n" ); document.write( "-2153 + 2041 + 112 = 0
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