Finding a model for a bouncing ball, Involves Quadratic Func

Kyle

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Oct 7, 2006
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Ok I'm in a Trig class but we're reviewing some Algebra at the moment and I got a worksheet with this problem that I need to solve before Tuesday. I will supply the question and all my information. If you want to contact me on AIM my s/n is emximer.

"A group of students dropped a rubber ball and measured the height in inches of the ball for each of its successive bounces. The results are shown in the table."

Bounce 1= 47 inches
Bounce 3= 26 inches
Bounce 4= 21 inches

a. Find a model for the data
b. What was the height of the ball before it was dropped?
c. What was the height of the ball on the 2nd bounce?
Basically I just need to know the model then I can find the rest.

OK there it is, the way I was told to go about it ( I forget the proper name for this formula/method EDIT: Quadtradic function?). Basically take the data and put it into a formula like such:
1. a+b+c=47
2. 9a+3b+c=26
3. 16a+4b+c=21
(To get these I did ax^2+bx+c=h where x= the bounce and h= the height)

And then I subtracted 3 from 2 to get 7a+b=-5
Then I subtracted 2 from 1 to get 8a+2b=-21

Then I multiplied 7a+b=-5 by 2 to get 14a+2b=-5, allowing me to subtract that from 8a+2b=-21 so I could isolate the variable 'a'. Then once getting a I subtracted it back into one of the above formulas to find the value of b, then subtracted both a and b into an earlier formula to find c. However everytime I did this I found my end model would only work for the first bounce or the first 2 bounces. I think I may be using the wrong formula or method here. Anyways heres the solutions I've found so far that fit some of the data but doesn't satisfy all of it.

f(x)= (11/2)x^2-32.5x+74 (Satisfys bounce 1 and 3, but not 4)
f(x)=(11/6)x^2+(107/6) + 82/3 (Satisfys bounce 1 only)

It would seem to me that the B value would have to be negative, but I dont know if this method will work for this problem because when the X gets larger it will gain height, which shouldn't happen in this problem.

Thank you for reading/helping, if you want more information or want me to clarify something please post here or contact me on aim (mentioned above) or email me.
 
Please don't post the same problem in more than one thread.

Anyway, is this the sort of model you were looking for?. I done this on Excel; Note the R^2.;That means the accuracy of the equation is as good as it gets. The closer to 1, the better; We're right on 1 :D .

ballsmallhe2.jpg


Calculate your 2nd bounce height from the equation.
 
Hey, thanks alot! Any chance someone could help me round those numbers to the nearest fraction, as that is what the teacher will be looking for and these numbers throw off my answer a tiny bit (When substituting 3 into it I get 25.9998 instead of 26)
Either way thanks a lot this has been a great help.
 
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