document.write( "Question 407925: An object is thrown from the top of a 144 ft building with an initial velocity of 128 ft per second. The height h of the object after t seconds is given by the quadratic equation h=-16t^2+128t+144/ when will the object hit the ground \n" ); document.write( "

Algebra.Com's Answer #287434 by nerdybill(7384) $\"\"$ $\"About$

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h=-16t^2+128t+144
\n" ); document.write( ".
\n" ); document.write( "h is height from the ground.
\n" ); document.write( "To find your answer set h to zero and solve for t:
\n" ); document.write( "0=-16t^2+128t+144
\n" ); document.write( "dividing both sides by -16:
\n" ); document.write( "0 = t^2+8t-9
\n" ); document.write( "factoring the right:
\n" ); document.write( "0 = (t-9)(t+1)
\n" ); document.write( "t = {-1, 9}
\n" ); document.write( "throw out the negative solution leaving:
\n" ); document.write( "t = 9 seconds \n" ); document.write( "

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