SOLUTION: I have a word problem that I have no idea how to do. can someone explain the steps to me? Please?? A ball is thrown vertically upward from the ground. Its distance in feet from

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: I have a word problem that I have no idea how to do. can someone explain the steps to me? Please?? A ball is thrown vertically upward from the ground. Its distance in feet from       Log On


   

Question 262561: I have a word problem that I have no idea how to do. can someone explain the steps to me? Please??
A ball is thrown vertically upward from the ground. Its distance in feet from the ground in t seconds is s=-16t^2+128t. After how many seconds will the ball be 192 feet from the ground?

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A ball is thrown vertically upward from the ground.
Its distance in feet from the ground in t seconds is s=-16t^2+128t.
After how many seconds will the ball be 192 feet from the ground?
:
Replace s with 192, and solve for t
-16t^2 + 128t = 192
-16t^2 + 128t - 192 = 0;
Simplify and change the signs, divide by -16
t^2 - 8t + 12 = 0
Factors to
(t-6)(t-2) = 0
Two solutions
t = 2 sec it will be at 192 ft on the way up
and
t = 6 sec it will be a 192 ft on the way down
:
Like this:
+graph%28+300%2C+200%2C+-6%2C+15%2C+-100%2C+300%2C+-16x%5E2%2B128x%29+
y is the height at x seconds