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May 11th, 2017, 04:24 PM   #1
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how to find When does Delbert's book pass him on its way down?

Hi I know it says to use a calculator but I am hoping and guessing it's not to hard to find this answer or help me find it.

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May 11th, 2017, 05:41 PM   #2
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$h=-16t^2+20t+300$

Time it reaches the highest point is at the vertex ... $t=\dfrac{-b}{2a}=\dfrac{-20}{2(-16)}=\dfrac{5}{8} \, sec$

$h\left(\dfrac{5}{8}\right)=-16\left(\dfrac{5}{8}\right)^2+20\left(\dfrac{5}{8} \right)+300=-\dfrac{25}{4}+\dfrac{25}{2}+300 = 306.25 \, ft$

Passes the starting point on the way down ...

$300=-16t^2+20t+300$

$0=-4t(4t-5) \implies t=\dfrac{5}{4} \, sec$
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May 15th, 2017, 01:01 PM   #3
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Thanks as always skeeter!
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