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April 27th, 2012, 09:09 PM   #1
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I think this is needing velocity found before anything can be done but I am completely lost. Any help would be greatly appreciated.

Set up an equation and then solve this problem:

An object is dropped from the top of a 400 foot-tall building. The height h (in feet) of the object t seconds after it is dropped is given by
h(t)= -16t^2 + 400

How long does it take for the object to hit the ground?
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April 27th, 2012, 09:14 PM   #2
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Re: Velocity?

You don't need the velocity, just set and solve for t. You will only need the positive root.

Divide through by 16 and arrange with the variable on the left:

Take the positive square root:

Hence, the object will hit the ground 5 seconds after being dropped.
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