a problem with a rocket being fired

[Guest]

A rocket at ground level is fired into the air. After one second that rocket is at 35 feet above the ground and after two seconds it is at 40 feet above the ground.
a. list three data points. remeber where the rocket started
b. use the data points to write three equasions, then use thier solution to write the equasion of the parabola that fits the data.
c. draw and label a sketch of this situation
d. figure out when the rocket will hit the ground.

what i have so far is the equasion ax^2+bx=c, and the points (0,0),(1,35), (2,40) for the points. i thought that i might be able to use a matrix, and if so could you tell me how that would work. if you could give me any more clues and ideas or steps that would be great or a link to anyone that can do that.

 

[stapel]

what i have so far is the equasion ax^2+bx=c

Why "ax² + bx = c", instead of the usual quadratic form, "ax² + bx + c = y"?

i thought that i might be able to use a matrix

If you use the usual quadratic form, yes. Plug the (x, y) values into the equation to obtain an equation in "a", "b", and "c". Then solve the resulting linear system. You can use a matrix for this.

could you tell me how that would work.

Which part? Do you not know how to solve systems of linear equations?

Please clarify. Thank you.

Eliz.

 

[Guest]

rocket problem

what im confused about now is that the answer for b. was f(x)=-15x^2+50x, and i dont understand how that is the answer for that
then for c. the answer is (10/3) sec is when the rocket will hit the ground. im just confused of how these answers work. could you give me any explanations

 

[tkhunny]

Plug in your three points.
This establishes three relationships.
Solve the simultaneous equations for a, b, and c.