• Dec 6th 2010, 03:34 PM
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.
• Dec 6th 2010, 04:15 PM
skeeter
Quote:

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?
• Dec 6th 2010, 04:29 PM
bat
Quote:

Originally Posted by skeeter
where did this problem come from?

From my exam review. Is this a problem? (Surprised)
• Dec 6th 2010, 04:35 PM
skeeter
Quote:

Originally Posted by bat
From my exam review. Is this a problem? (Surprised)

never had a rocket problem where the trajectory is an open-upwards parabola ...
• Dec 6th 2010, 04:44 PM
bat
Quote:

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.
• Dec 6th 2010, 04:59 PM
skeeter
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.
• Dec 7th 2010, 12:42 AM
jgv115
mmm.. sorry for going off topic but how come this is in the precalculus forum?