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Homework Help: Biomechanics Question - Please Help

  1. Mar 31, 2005 #1
    Biomechanics Question - Please Help!!!!

    My question is: You and your 100 kg partner are stranded in space 100m from your spaceship, you are running out of air and you have no equipment at all to help you get back. You are fine but your partner is badly injured and unable to move at all. Your partner is directly between you and the ship.

    Using the concepts of conservation of linear and angular momentum, explain how you could get back to your spaceship in a reasonable degree of control facing towards it so that you can fly the spacecraft to retrieve your partner.

    Any help would be greatly appreciated! Thanks in advance!
  2. jcsd
  3. Mar 31, 2005 #2
    If you had something to throw it would be a lot easier to do, all I could think about is wiggle in some funky way to try to gain some speed.

    Wheres the biomechanics in this?
  4. Mar 31, 2005 #3
    Easy, you just push off your partner, and go get him later. Am I missing something ?
  5. Mar 31, 2005 #4
    Well youre facing the ship, but your partner is between you and the ship, facing you. I thought if you could somehow spin with him to trade places with him it might work, but as it stands, he is in your way.

    Any help is appreciated! Thanks!
  6. Mar 31, 2005 #5
    I interpreted directly between as half way between, doesnt that make sense? If he's 50m away you can't do much. If you can reach him, pulling him behind you will pull you towards the ship.
  7. Mar 31, 2005 #6
    I attached the picture for the question to clear things up (#2). I also need help with #3 if anyone knows angular momentum well. Thanks!!!

    Attached Files:

  8. Mar 31, 2005 #7
    #2: Grab your partner and rotate yourselves until the line between the two of you is perpendicular to the line from the spaceship to you. At this point let go, your tangential velocity is aimed right at the spaceship.

    Can't read #3
  9. Mar 31, 2005 #8
    thanks whozum. can you just start spinning in space tho? wouldn't you have to initiate it somehow? #3 is asking if the angular momentum is shown by the big arrow, what direction is the guy twisting and somersaulting and name 2 ways to stop the rotation. thanks again!
  10. Mar 31, 2005 #9
    You can apply a force in space. You can apply a torque in space, if you apply the right torque ideally you would end up going in a circle, if you let go at the right time your centripetal force will be 0 and your tangential velocity will aim directly at the ship. Moving your arm is applying a force. Why wouldn't you be able to do stuff with it?
  11. Mar 31, 2005 #10
    Ok, this is true. Now what exactly could you and the partner do to create a torque to start the spinning. Remember, I need to be facing the ship when I get there and I need to be in control of my speed (preferably slowing down). Thanks :)!
  12. Mar 31, 2005 #11
    You can't slow down, there are no forces acting on you once you let go of your body. You can pull him really slow which would make your velocity low. If you grab your partner and shift him to the left but hold on, the result will be both of you travelling in a circle, thats travelling in a much smaller circle. Dont worry about this part. The only way I can think of is as you let go of him try to push off in a manner that will turn you towards him yet not induce a spin.
  13. Mar 31, 2005 #12


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    Gold Member

    I can't open that, but I'll go with the typed question. The only things that I can think of are:
    a) If you're buddy is within reach, throw him away from the ship and let the reaction accelerate you toward it. Then fly over and get him while you can still find him.
    b) Use some of your remaining air as a rocket.

    edit: If you're looking for specific formulae or laws or the like, then you'll have to wait for someone else to respond. I don't know 'em. :redface:
    Last edited: Mar 31, 2005
  14. Mar 31, 2005 #13
    Didnt we already solve this problem in your other thread
  15. Mar 31, 2005 #14
    ok thanks....this is really frustrating me...im supposed to incorporate the laws of angular and linear momentum but dont know how. my prof says it isnt easy, so there must be a trick to it maybe...
  16. Apr 1, 2005 #15

    Doc Al

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    Staff: Mentor

    I merged the two threads.
    Please do not double post!
  17. Apr 1, 2005 #16
    I attached here the questions I need help with. Please help with #2 and #3!! Thanks!

    Attached Files:

  18. Apr 1, 2005 #17
    Well why dont you start by telling us the laws of angular and linear momentum and their relatinoship to this problem.
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