Thread: Quadratic problem

Hey guys I need a little help with this problem.

A rocket is fired from the ground into the air. After 10 seconds, the rocket is 150 feet in the air. After 50 seconds, the rocket is back down to 90 feet, and after 112 seconds, 30 feet.

1. Write the equation in standard form. This one I put it into a matrix and got: y = .005x^2-1.813x+167.609

2. how many seconds will the rocket be back to the ground?
No idea how to solve this.

Originally Posted by bat

Hey guys I need a little help with this problem.

A rocket is fired from the ground into the air. After 10 seconds, the rocket is 150 feet in the air. After 50 seconds, the rocket is back down to 90 feet, and after 112 seconds, 30 feet.

1. Write the equation in standard form. This one I put it into a matrix and got: y = .005x^2-1.813x+167.609

2. how many seconds will the rocket be back to the ground?
No idea how to solve this.

where did this problem come from?

Originally Posted by skeeter

where did this problem come from?

From my exam review. Is this a problem?

Originally Posted by bat

From my exam review. Is this a problem?

never had a rocket problem where the trajectory is an open-upwards parabola ...

Originally Posted by skeeter

never had a rocket problem where the trajectory is an open-upwards parabola ...

You're right... Neither have I, am I doing something wrong?
I keep on getting an upwards parabola.

you're not doing anything wrong ... as far as the math goes, your calculated quadratic fits all three given points.

set y = 0 and use your calculator to find the time for the zero height.

ask about it when you go over it in class ... bogus problem imho.

mmm.. sorry for going off topic but how come this is in the precalculus forum?

Isn't quadratics algebra?

Originally Posted by jgv115

mmm.. sorry for going off topic but how come this is in the precalculus forum?

Isn't quadratics algebra?

because it's fitting a curve to a set of points.