SOLUTION: Hi PLEASE HELP ME!! I really do NOT know what i'm doing!! I need HELP! Help would be greatly appreciated! here is the problem and directions: Use the formula h=rt-4.9t^2 where h is

Question 23434: Hi PLEASE HELP ME!! I really do NOT know what i'm doing!! I need HELP! Help would be greatly appreciated! here is the problem and directions: Use the formula h=rt-4.9t^2 where h is in meters and the formula h=rt-16t^2 where h is in feet. The Problem: A ball is thrown upward with an intial speed of 24.5 m/s. when is it 19.6 m high? (Two answers)
Please help me, i'm desperate, i just cannot figure out this assignment, i'm having a lot of trouble! Thanks!
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
height = -4.9t^2+(rate)t
h = -4.9t^2+24.5t
Let height be 19.6 m; what is the time?
19.6 = -4.9t^2+24.5t
-4.9t^2+24.5t-19.6=0
This is a quadratic with a=-4.9, b=24.5, c=-19.6

Solved by pluggable solver: SOLVE quadratic equation with variable

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=216.09 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 1, 4. Here's your graph:

So, the height is 19.6 meters after 1 second
and after 4 seconds.
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