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Finding Mass without using any scale

  1. Jan 7, 2007 #1
    Hi,I had this problem which I cannot answer. I would appreciate if someone could help me out.

    Here's the problem -

    1. The problem statement, all variables and given/known data

    In the labaratory,you are asked to determine the mass of a meterstick without using a scale of any kind. In addition to the meterstick you may use :

    • Set of known masses
    • a fulcrum upon which the meterstick can be mounted and pivoted
    • four weight hangers
    • string
    • tape
    • stopwatch

    1.Briefly list the steps in your procedure that will lead you to the mass of the meterstick.

    2.Show calcualtions you would perform to find the mass of a meterstick.


    Would we use the fulcrum and tie it up with the string and the meterstick? on the other side,hang one of the weight hangers and start putting in the masses and wait till the thing stablizes?

  2. jcsd
  3. Jan 7, 2007 #2


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    Sounds good to me. I'm sure you'll include more detail in your write up, such as measuring the points where you place the fulcrum and the weights etc.
  4. Jan 7, 2007 #3
    just wondering but why does the question say we can use upto 4 weight hangers? whats with 4? Arent 2 fine with any kind of experiment?
  5. Jan 7, 2007 #4


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    I'm sure the whoever set the question had some sort of experiment in mind that neither of us could imagine; but your method is a valid solution to the problem set.
  6. Jan 7, 2007 #5


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    I'm not sure that fits the conditions. You said "a fulcrum upon which the meterstick can be mounted and pivoted" but it sounds like you are using the string to hang the meterstick on one side and the masses on the other.

    Perhaps better: attach the meterstick to the fulcrum not at the center. Hang masses on the short end to balance. That will allow you to find the difference in mass of the two ends and, since you know their lengths, the density of the meterstick and so its mass.

    Another way, if this is a metal meterstick is to attach one end firmly to the wall so the meterstick extends horizontally, give the free end a good "whack" and use the stop watch to time its vibrations.
  7. Jan 7, 2007 #6

    Gib Z

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    Teachers often give more than required to make students think something is harder than it really is. The more detail there is, the harder it seems.

    Some friends in the grade above me told me of a test question where they give you lots of details on a mound of dirt. They gave the mass, the dimensions, even the color, and the question was how deep in the hole. The vast majority assumed the dirt was digged out from the hole and they had to deduce the answer. Of course, they couldn't, so most gave guessed. Only 7 people said there was no hole. :D
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