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Variable Mass

  1. Sep 11, 2014 #1


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    Hello everyone.

    I've been struggling with how to deal or solve questions that include variable masses. Considering the method I usually try to solve with, it either gets me lost or just makes things complicated and doesn't work often to me. :P

    I was wondering if you guys could help me out and tell me what is the best way to approach questions with variable mass and how to actually solve them. examples would also help a lot.

    Thank you!
  2. jcsd
  3. Sep 11, 2014 #2


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    Gold Member
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    Yes, "examples would help a lot". How about showing one? That is, show a specific problem you are having trouble with.
  4. Sep 11, 2014 #3


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    Staff: Mentor

    One of our homework forums would be the best place to do this, even if it's not an actual assignment for a class. The "homework helpers" are used to helping people find errors and misconceptions.
  5. Sep 11, 2014 #4


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    Usually, the mass has to go somewhere, so some of the momentum goes with it.
  6. Sep 11, 2014 #5


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    If m is variable then "F= ma" (force equals mass times acceleration) becomes "[itex]F= \frac{d(mv)}{dt}= ma+ v\frac{dm}{dt}[/itex]".
  7. Sep 11, 2014 #6


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    First of all thank you all for the replies. As soon as I get troubled again with a problem, I'll make sure to post it here before looking at its solution.
  8. Sep 11, 2014 #7


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    Staff: Mentor

    Not quite EXACTLY here in Classical Physics, I hope :smile:
    Post it to one of our homework forums.
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