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Homework Help: General Energy conservation question

  1. Oct 25, 2009 #1
    This isn't really a homework question, so I'm hoping I can just get a straight answer from someone (although it is related to questions).

    I realize that you can choose U = 0 anywhere you want in a gravity-related problem, ideally choosing a place where it is easiest to manipulate mgy values.

    However, in a problem where both a spring force and gravity are of concern (i.e. where a spring is at an angle or hanging vertically), can you choose two different U = 0 positions?

    That is, can you choose the lowest point to be Ugrav = 0 and the point where the spring is relaxed to be Uspring = 0, even if the two places are not the same y value? Or, do both PE's have to align?

  2. jcsd
  3. Oct 25, 2009 #2


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    Homework Helper

    Yes, choose the spring U to be zero when relaxed and the gravitational energy zero height entirely separately.
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