April 27th, 2012, 09:09 PM  #1 
Newbie Joined: Apr 2012 Posts: 14 Thanks: 0  Velocity?
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 foottall 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? 
April 27th, 2012, 09:14 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 461 Math Focus: Calculus/ODEs  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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