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Planet X

  1. Oct 30, 2012 #1
    The escape velocity on Planet X is the speed the rocket needs in order to never fall back down again in a universe in which X is the only object. In order for the rocket to not fall back down, its velocity to never become negative, how far away does the rocket have to be when the velocity is 0?

    What are the steps to solving a problem such as this one?
     
  2. jcsd
  3. Oct 30, 2012 #2

    russ_watters

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    Staff: Mentor

    Welcome to PF!

    There's nothing to solve there, it is just a matter of understanding the implications of escape velocity. I'd start by reading the wiki on it...
     
  4. Oct 30, 2012 #3
    So all in all, it ends up being a trick question? Lol
     
  5. Oct 30, 2012 #4
    It depends if the speed is the rocket or the rocket is the speed or some weird quantum superposition of speed/rocket states.
     
  6. Oct 30, 2012 #5
    Our prof gave us a hint and told us to call the position Xf. He indicated that the answer was right under our noses.

    Which led me to believe that there was some deception involved.
     
  7. Oct 30, 2012 #6

    russ_watters

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    Staff: Mentor

    I don't see it as a trick question, no. This is a common question people have/don't understand regarding escape velocity.

    Did you find the answer?
     
  8. Oct 31, 2012 #7
    According to the escape velocity equation, the distance from the centre of Planet X would need to be infinite to achieve a velocity of 0. It could always reverse it's thrust to achieve a velocity of 0, but the question says it can't. OR considering the definition of escape velocity and the common misconceptions, the answer is probably the rocket would have to be inside the planets centre, where r = 0.
     
    Last edited: Oct 31, 2012
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