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April 18, 2015

April 18, 2015

Posted by **Paula** on Friday, February 15, 2013 at 10:32pm.

- algebra -
**Reiny**, Friday, February 15, 2013 at 11:11pmheight = -4.9t^2 + 15t + 26

When the rock is 5 metres above the water,

5 = -4.9t^2 + 15t + 26

4.9t^2 - 15t - 21 = 0

t = (15 ± √636.6)/9.8

= 4.1052 seconds or a negative

After appr 4.1 seconds, the rock is 5 metres above the water.

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