Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Finding a position vector

  1. Feb 25, 2012 #1
    Finding a position vector....

    1. The problem statement, all variables and given/known data
    A spaceship is traveling with acceleration a(t)=<e^(t) , t , sin2t>. At t=0, the spaceship was a origin r(0)=<0,0,0> and had an initial velocity of v(0)=<1,0,0> Find the position of the ship at t=pi


    2. Relevant equations

    uhhh...

    3. The attempt at a solution

    I figured I'd work backwards with the acceleration vector given to find the velocity and position vectors, then put the t=pi into the position vector I find.

    So, v(t)=<e^(t) , (1/2)t^(2) , -(1/2)cos(2t)>
    Then r(t)=<e^(t), (1/6)t^(3) , -(1/4)sin(2t)>

    But this doesn't seem right to me because when I put in the given t=0 into my v(t), I get <1,0,-(1/2)> not the <1,0,0> like the problem says. I'm approaching this problem wrong, aren't I?
     
  2. jcsd
  3. Feb 25, 2012 #2
    Re: Finding a position vector....

    No, you are doing fairly well. What would happen if you added a constant to the velocity?
     
  4. Feb 25, 2012 #3
    Re: Finding a position vector....

    Okay, I have it figured out.

    v(t)=<e^(t) , (1/2)t^2 , (-1/2)cos(2t)+(1/2)> So that V(0)=<1,0,0>

    Then, I find r(t) which is equal to <e^(t)-1 , (1/6)t^3 , (-1/4)sin(2t)+(1/2)t> So that r(0)=<0,0,0>

    Then I plug in pi into my r(t) which comes out to be r(pi)=<e^(pi)-1 , (1/6)pi^3 , (pi/2)> Please tell me this is right. :)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook