- #1
dantechiesa
Homework Statement
Your cousin has built a model rocket that she wishes to launch in your backyard. You're a little worried by this, and ask her for details.
She tells you, when I launch the rocket straight upwards, the acceleration will be 3.5g = (3.5*9.8m/s^2) for 4.3 seconds, then burn out.
A) What is the max height the rocket will reach
and specifically, what I need help with, what will the time from launch until the rocket returns to the ground.
Homework Equations
V^2 = V0^2 +2ad
d = v0t + .5at^2
3. The Attempt at a Solution
So, what I am having trouble with is calculating the time the rocket spends in the air after its acceleration fuel burns out (after 4.3 seconds)
Phase 1: the initial 4.3 seconds
Phase 2: the remaining time it spends in the air
Phase 3: the rocket falls to the ground.
Right when the first phase ends, I was able to calculate its
Vf = 147.49m/s^2 (subsequently is the V0 for phase 2)
d = 317.1035m and phase 2 distance = 1102.5m
However, when I try to calculate time, the quadratic formula isn't giving the correct time.
I input into my calculator
1102.5 = 147.49t - 4.9t^2
0 = -4.9t^2 + 147.49 - 1102.5
This is giving 2 positive roots.
What have I done wrong?