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Homework Help: "best" value for volume of a box

  1. Sep 23, 2014 #1
    1. The problem statement, all variables and given/known data
    I'm given length, width and height of the box, all have uncertainties.

    2. Relevant equations

    3. The attempt at a solution
    I've tried V=lwh, wasn't correct. Then V=lwh x (1 + relative uncertainty), wasn't correct. I just have no idea what the "best" value of a box is, my lab manual doesn't say anything about it, and I can't find anything on google either and I'm running out of tries. Appreciate any help!
  2. jcsd
  3. Sep 23, 2014 #2

    Simon Bridge

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    You need to define "best value" for this problem - what does that mean?

    Please provide the complete problem statement.
    If you have ##l\pm\sigma_l##, ##w\pm\sigma_w## and ##h\pm\sigma_h## as independent measurements of the dimensions of a rectangular box, then the volume of the box is ##V=lwh\pm\sigma_V##.

    So if that is not correct (how do you know?) then there is some information missing from the problem statement, or the solution attempt. i.e. how did you evaluate ##\sigma_V##?
  4. Sep 23, 2014 #3
    That's the thing..I don't know what the "best" value is, and nowhere I've looked has told me what it means. And it's for an online assignment which I have 10 tries for, so it tells me whether the answer is right or wrong.

    EDIT: Never mind. I can't believe how stupid the mistake I was making was..I just wasn't paying attention to the units. Measurements were given in cm, question wanted m^3. Sorry for wasting your time.
  5. Sep 23, 2014 #4

    Simon Bridge

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    No worries - sometimes talking to someone else is what it takes to see the obvious right under your nose :)

    BTW: whenever you have an answer you know is wrong - you should say how you know.
    The assessment of the problem changes whether you got an answer different from a model answer, and answer that a human marked wrong, and an answer that a computer marked wrong.

    You should also always show you working and reasoning ... seeing correct calculations and a "the computer rejected the result" would have got you specific and helpful advise right away.
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