# Re: I need help with quadratic functions....

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Posted by Brad Paul on October 16, 2002 at 07:59:52:

In Reply to: I need help with quadratic functions.... posted by Alison on October 15, 2002 at 21:22:25:

: Im not sure if anyone can help me...but right now im working on quadratic functions when they're used with projectile motion. i know the formula is
: h(t)=-1/2g(t^2)+Vt+H. My problem says:

: "a baseball is thrown up with an initial velocity of 24.5 meters per second. the ball is released at a point 49 meters above the surface of a baseball field."

: then the questions are
: 1) what is the height of the ball in 2 seconds?
: 2) when is the ball again at 49 meters?
: 3) When does the ball reach the ground?

: My problem is i dont know what to plug in where when i need to find out what the hight of the ball after 2 seconds is. the other problem i have is what do i do when i need to find out when the ball will be at the same height it started at again... and where and what do i plug in to find out when the ball reaches the ground. if anyone could help me i would be so gratefull! thanks!

: :)Alison:)
Your h(t) is the height of the ball as a function of time. Height is
measured from the ground. This may seem obvious but it is worth
saying. How high is the ball just as it is thrown (t=0)? The answer is
H. Plug t=0 into your equation and what do you get? Just H.

1) Just plug in your value for time.

2) The question is when does h(t)=H We know t=0 is a solution but
there is another. Which can be found (along with t=0) by solving:
H=1/2 g t2+Vt+H for t.

3) How high above the ground is the ball when it hits the ground? This
is one of those dumb questions with a very simple answer. Zero. So
lets use that info to find out when.

h(t)=0=1/2 g t2+Vt+H
solve for t

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