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Pulley problem (Two masses acting on a third body)

  1. Nov 8, 2012 #1
    First off,I would like to apologise for not introducing myself.
    I have yet to find that certain part of the forum,but if the mistake was on my part,mods please direct me.

    Now to go to the real issue.

    This is something I've long "gotten over",meaning it was in the introductory lessons in college,I forgot about it,but honestly it never "clicked".

    My teacher gave me a real bad explanation.

    In the attached picture,the two objects with m=5kg ,are pulling a third object,or to be precise a dynometer.
    What amount of force will the dynometer show?

    The teachers answer was 50Nm(49.05Nm) ,but somehow the number 98.1Nm is going around my brain.

    I don't think I have enough credentials to contradict him,and honestly don't know If I am right,doubt it somehow,but there's this part of my brain that just can't let it go.

    So ,if you would be so kind as to give me the correct answer and a good explanation.

    Thank you very much.

    (Also,I apologise for any technical terms I might have misspelled or missed entirely,English is my second language)

    Attached Files:

  2. jcsd
  3. Nov 8, 2012 #2


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  4. Nov 8, 2012 #3

    I gave it a good solid thought for the past hour or so,and gotten to the same conclusion,but was still a bit iffy,this assured me though.

    I'm actually a bit ashamed now,strange how sometimes we can't even grasp the simplest of things but yet try to go for the more complex.

    Oh well,all a part of the human experience...

    EDIT: To elaborate my train of thought,in case someone else might be going through the same konundrum.
    Since I expected 49.05Nm from one weight,98.1 was an immediate thought linked to two weights,but it took me an imaginary wall to realize that the weight was,let's put it,all ready there,just in a different form.
    And of course then it hit me that I was measuring the force of reaction and not the actual weight.
    Last edited: Nov 8, 2012
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