Determine the acceleration of a rocket.

azizlwl

1. Total displacement is zero.
2. Rocket travelled with 2 constant acceleration +a and -g

ehild

If you like you can call the upward acceleration "a-g". Then "a" would be the acceleration of the rocket in free space. But the problem says that the rocket flyes upward with constant acceleration a.

The rocket starts from zero velocity. Have you seen the launch of a rocket? What is your vo then?

The end of the first stage is when the fuel burns out. It does not mean that the rocket reaches the top height then: it will rise till the velocity becomes zero, but its acceleration is -9.81 m/s^2 during this time, and this rising motion also belongs to the second stage.

ehild

Squizzel

OK so my first equation would v/30 = a because V = Vo + at and Vo = 0.

ehild

What is v/30?

ehild

Squizzel

V/t = a for the first phase t is 30.

ehild

So the acceleration during the first phase is a, and the velocity after 30 seconds is v=30a. What is the hight of the rocket at that instant?

ehild

Squizzel

Y = 1/2 at,^²

Squizzel

To find the V for the first equation, I know that it is the initial velocity in the second equation.

so for the 2nd equation I got V = Vo + at

0 = Vo + (-9.81)(270) v = 0 because that is when the rocket lands. with this equation I got that Vo = 2648.7

Squizzel

Plugging that back into my first equation I get that V = a(30) and a = 88.3

roovid

what is did was incorrect
sorry

ehild

The velocity is not zero when the rocket lands.

For the second stage, vo = 30a and yo =30²a/2=450a.
The second stage is under the effect of gravity alone, "free fall" but the initial velocity is upward,so the rocket will rise with decreasing velocity. After the velocity becomes zero, the rocket turns back and begins falling down.
The displacement is y=yo+vot-9.81/2 t². If t=270s, the rocket reaches the ground, y=0. Substituting vo=30a and yo=450a, t=270, you get an equation for a.

ehild

roovid

srry incorrect wrking was put here

ehild

The rocket will not turn back immediately as the fuel burns out. It will rise till the velocity becomes zero. So the real time of fall is less than 270 s.
"free fall" means motion under the gravity of Earth alone.

ehild

roovid

oh my bad then
i thought for calculation purposes only they wanted u to assume tohe rocket fell aft fuel ran out
thanks for clearing up the free fall term for me

ehild

How can a rocket change its velocity to zero in no time, without fuel??? Even the problem maker can not assume nonsense....

ehild

roovid

lol i kno
but some of the question i am doin are makin me assume some weird stuff
for basic calculation purposes
sorry.my error
thnx fr the correction again

ehild

You are welcome.

ehild