Freefall

[spatel600]

Basically I have worked this problem over and over:

http://labphysics.uncc.edu/cgi-bin/QuizP/QGenGrd_F.cgi/uu?4

Note: On this site the numbers change
The numbers I have on the print out is Upward Accel: 20m/s^s
and 31.6s the engine shuts off


So this is what i have done so far:

y-yo = vot + 1/2 at^2

I used this equation to find max height y

I found initial velocity by v=vo + at

The answers I have is highest height is 9985.6m
Initial Velocity is 632 m/s

I am really stuck. Any help would be appreciated.

[Parth Dave]

i would think of it in three parts:
1. what happens in the first 45.3 seconds?
2. what happens from that point until it reaches its max height?
3. what happens the rest of the way?

look at the velocity, displacement, time in each section.

[spatel600]

I have been looking at that. Its just that I don't remember what to do. I wish I knew but the last time we did this stuff was a few years back. Thanks

Still stuck.....please help

[Parth Dave]

given the acceleration you can figure out the displacement in the first 45.3 seconds, correct? (via d = vt + (1/2)at^2) You could also figure out your final velocity in this section, which would then become your initial velocity for the next section.

Given the initial velocity in the section (whatever you got in the last part), the final velocity (0, because the max height implies 0 velocity), and the acceleration you can then figure out the time it takes to reach that velocity. (via V = V(initial) + at). Which will than allow you to figure out the displacement. (same formula as above).

At this point you should have got the max height for the rocket. On the return trip down the rocket will have constant acceleration (g = acceleration due to gravity) and it will also have an initial velocity of 0 (from the last section). From that you can figure out the time it takes to reach the ground(again using the same displacement formula as above)[part b]. Now you have the time the rocket takes to reach the bottom and the acceleration. Thus you can figure out the final velocity as it hits the ground.