Question 164026: A rock is thrown from the top of a buliding. The distance, in feet, between the rock and the ground t seconds after it is thrown is given by D=-16t^2-4t+400. How long after the rock is thrown is it 370 feet from the groun? show work thanks
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A rock is thrown from the top of a buliding. The distance, in feet, between the rock and the ground t seconds after it is thrown is given by D=-16t^2-4t+400. How long after the rock is thrown is it 370 feet from the groun?
------------------------
370 = -16t^2 - 4t + 400
-16t^2 - 4t + 30 = 0
------
-8t^2 - 2t + 15 = 0
-----
Use the quadratic formula to get:
t = [2 +- sqrt(4 - 4*-8*15)]/-16
t = [2 - sqrt(484)]/-16
t = [2 - 22]/-16
t = -20/-16 = 5/4 second
==============================
Cheers,
Stan H.
|
|
|
