SOLUTION: The height of a rock above the ground is given by the equation h=-16t^2+24t+16. T is the time in seconds after the rock is thrown. It is thrown upward from a platform 16 feet above

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: The height of a rock above the ground is given by the equation h=-16t^2+24t+16. T is the time in seconds after the rock is thrown. It is thrown upward from a platform 16 feet above      Log On


   

Question 1027481: The height of a rock above the ground is given by the equation h=-16t^2+24t+16. T is the time in seconds after the rock is thrown. It is thrown upward from a platform 16 feet above the ground. After how many seconds is the rock back to a height of 16 feet?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+h+=+-16t%5E2+%2B+24t+%2B+16+
I want 2 solutions for +h+=+16+
One of the solutions is when +t+=+0+
+h+=+-16%2A0%5E2+%2B+24%2A0+%2B+16+
+h+=+16+
---------------
Set +h+=+16+ again
+h+=+-16t%5E2+%2B+24t+%2B+16+
+16+=+-16t%5E2+%2B+24t+%2B+16+
Subtract +16+ from both sides
+-16t%5E2+%2B+24t+=+0+
+t%2A%28+-16t+%2B+24+%29+=+0+
+-16t+%2B+24+=+0+
+16t+=+24+
+t+=+1.5+
In 1.5 sec, the rock is on it's way down
and is at a height of 16 ft
------------------------
Here's the plot:
+graph%28+400%2C+400%2C+-3%2C+3%2C+-2%2C+30%2C+-16x%5E2+%2B+24x+%2B+16+%29+