...if not all of you. but i am a dumb ass (also can you explain how you did it?)

A model rocket accelerates upward from the ground with a constant acceleration, reaching a height of 91 m in 4.2 s.

What is the acceleration (in m/s 2)?
What is the speed (in m/s) at a height of 91 m?

8/31/2006 5:06:25 PM

x = (1/2) a t^2
v = a t

8/31/2006 5:09:40 PM

101101110110001

8/31/2006 5:10:57 PM

^^ i cant use that first one cause i dont know a...right?

8/31/2006 5:13:57 PM

e^(pi * i)

8/31/2006 5:19:14 PM

^^ you know x and t, so you can solve for a

8/31/2006 5:29:41 PM

^^^thats the point. you don't know "a", so you find an equation with variables that you know and use that to solve for the unknown.

i really enjoyed all the kinematics stuff from ap physics. this brought me back.

[Edited on August 31, 2006 at 6:06 PM. Reason : .]

8/31/2006 6:06:06 PM

Thanks for the help all.

8/31/2006 6:07:57 PM

I'll help you...

If A is constant, integrate to get velocity:

A(t) = A %A is a constant (acceleration)

V(t) = At + V0 %V0 is initial velocity (zero in this case)

Integrate again to get position:

D(t)= (1/2)A(t^2) +V0t + D0 %Do in initial displacement (zero in this case)

t in all cases is time

Since the rocket started from rest at the ground V at time zero, or V(0)=0

In fact, you don't really need all that math to solve this problem.

Since acceleration is constant and you started from rest, your average speed is one half your final speed. (work with the above equations to see why) Your average speed is your [total displacement / net time]. Double that value for your speed at time 4.2s. Once you know your final speed you can calculate your acceleration. Acceleration is your cange in speed per unit time. Thus, your acceleration in this case is your [final velocity / time it took to get to the final point].

If you can't solve the problem from what I've given you, drop out of college. (not a joke, just trying to save your parents money)

8/31/2006 6:19:26 PM

this isn't rocket science

9/1/2006 9:50:47 AM

^ You come in a day late to make a bad joke.... go back to chit-chat.

9/1/2006 10:45:12 AM

tjoshea answered the question in the second post to the thread

9/1/2006 12:00:49 PM

^ and the kid obviously understood the answer

9/1/2006 3:52:19 PM

Quote :

"^^ i cant use that first one cause i dont know a...right?"

jesus christ

9/2/2006 11:47:33 AM