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Some Concept Questions

  1. Nov 14, 2009 #1
    Hi

    I was wondering if anyone could explain why the momentum of the center of mass of a system is different than the sum of the independent momentums of every object.

    I also don't understand the concepts of the first and second moment of area. I would appreciate it if someone explained it to me.

    Thanks for any help that you can provide
     
  2. jcsd
  3. Nov 14, 2009 #2

    Doc Al

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    Staff: Mentor

    Why do you think it's different?
     
  4. Nov 14, 2009 #3
    Because on a question for my homework, which asked for linear momentum of the system, I got two different answers when i did the momentum of each separately than doing the momentum of the center of mass.
     
  5. Nov 14, 2009 #4

    Doc Al

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    Staff: Mentor

    I'd have to see the details, but I suspect you made an error.
     
  6. Nov 14, 2009 #5
    If they are indeed the same then I probably did. I'll try to work out what I did wrong. Thanks.
     
  7. Nov 14, 2009 #6
    I think I figured out what I did but I don't really understand why. I did the change in position of the center of mass, divided it by the time interval, and multiplied the result by the total mass of the system and I got a very off answer. Can anyone explain why I can't do it this way? Thanks
     
  8. Nov 15, 2009 #7

    Doc Al

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    Staff: Mentor

    You can do it that way. In order to find out where you went wrong, please describe the actual problem.
     
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