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September 20, 2014

September 20, 2014

Posted by **lola** on Friday, July 13, 2012 at 9:29pm.

- Math/calculus -
**Reiny**, Friday, July 13, 2012 at 11:45pmh(t) = -3t^3 + 6t^2 + 27t

h' (t) = -9t^2 + 12t + 27

= 0 for a max/min of h(t)

divide by -3

3t^2 - 4t - 9 = 0

t = (4 ± √124)/6

= appr 2.523 or -1.18 , which we reject since time cannot be negative

h(2.523) = ..... you do the button-pushing.

initial velocity ---> t = 0

h' (0) = 27 ft/sec

when t=2

h'(2) = -9(4) + 12(2) + 27 = 15

average velocity in first 2 seconds:

h(0) = 0

h(2) = -3(8) + 6(4) + 27(2) = 54

avg vel = (54-0)/(2-0) = 27 ft/s

check my arithmetic

- Math/calculus -
**lola**, Saturday, July 14, 2012 at 11:20amThank you very much but how do I calculatethe speed at which it crashes to the ground? I got38.181 for the max height do I start from there?

Thanks again, going through the calculations you gave makes it easier to understand how I use the formulas. I am never sure when to use first derivatives, 2nd etc-when to factor etc you have been very helpful.

lola

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