SOLUTION: If a stone is tossed from the top of a 170 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 � 10t + 170, where t is in seconds, and height

Question 613929: If a stone is tossed from the top of a 170 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 � 10t + 170, where t is in seconds, and height is in meters. After how many seconds will the stone hit the ground? Round to the nearest hundredth�s place; include units in your answer.
please this is the only problem I need help with. I just don't understand!
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!

I'll plot this because the plot shows exactly what the
stone is doing at any time after it's thrown.

You can see that at , the height, , is 170.
What you are being asked is " How many seconds have passed
after stone is thrown until the stone hits the ground?"
Note that the stone is not thrown straight up and landing at
the 170 m height of the building. It is landing 170 m below this
at the ground level.
At ground level, , so I can now say

Now I can use the quadratic formula to solve for

sec ( rounded off )
The stone hits the ground in 3.69 seconds
Note that I had to use the negative root in the formula
because that gave me (-)/(-) or positive time.
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