document.write( "Question 210708: A ball is shot into the air. It's height , h in metres after t seconds is modeled by h=-4.9t^2 + 30t +1.6. How long to 2 decimal places will it take the ball to reach a height of 35m? \n" ); document.write( "

Algebra.Com's Answer #159218 by Earlsdon(6294) $\"\"$ $\"About$

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You need to find at what time, t, will the height, h, is equal to 35 metres.
\n" ); document.write( "Set h = 35 and solve for t.
\n" ); document.write( " $\"35+=+-4.9t%5E2%2B30t%2B1.6\"$ Subtract 3 from both sides.
\n" ); document.write( " $\"-4.9t%5E2%2B30t%2B33.4+=+0\"$ Solve this quadratic equation using the quadratic formula: $\"t+=+-b%2B-sqrt%28b%5E2-4ac%29%29%2F2a\"$ In this equation, a = -4.9, b = 30, and c = -33.4. Make the appropriate substitutions into the formula:
\n" ); document.write( " $\"t+=+%28-30%2B-sqrt%2830%5E2-4%28-4.9%29%2833.4%29%29%29%2F2%28-4.9%29\"$ Evaluate:
\n" ); document.write( " $\"t+=+%28-30%2B-sqrt%28900-%28-654.64%29%29%29%2F%28-9.8%29\"$
\n" ); document.write( " $\"t+=+%28-30%2B-sqrt%281554.64%29%29%2F%28-9.8%29\"$
\n" ); document.write( " $\"t+=+%28-30%2B-39.43%29%2F%28-9.8%29\"$
\n" ); document.write( " $\"t+=+%28-30%2B39.43%29%2F%28-9.8%29\"$ or $\"t+=+%28-30-39.43%29%2F%28-9.8%29\"$
\n" ); document.write( " $\"t+=+-0.962\"$ or $\"highlight%28t+=+7.08%29\"$ Discard the negative solution
\n" ); document.write( "It will take 7.08 seconds for the ball to reach a height of 35 metres. \n" ); document.write( "

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