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Pulley + spring balance problem.

  1. Feb 11, 2016 #1
    1. The problem statement, all variables and given/known data
    A light spring passing over a smooth pulley carries a spring balance of mass 1 kg and two weights of masses 1 kg and 2 kg. the reading on the balance will be

    2. Relevant equations
    3. The attempt at a solution

    to my knowledge whatever the tension above the spring balance the reading will not change, it is only affected by the reading below it. Therefore I considered
    reading = weight of spring balance + 1N
    Reading = 20N
    But I'm not sure whether this is the right approach. Should the mass of spring be considered? Or will there be some sort of acceleration taking place?

    Thank you.
     

    Attached Files:

  2. jcsd
  3. Feb 11, 2016 #2

    BvU

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    Hi,

    You want to draw a free body diagram of the spring balance.

    Is your 1 N a typo? DId you mean 10 N ?

    To help you form an idea of the situation:
    Suppose the spring balance + 1kg weight hangs from a nail in the wall.
    What does the balance reading show ?
    What is the force on the nail ?​
     
  4. Feb 12, 2016 #3
    image.jpg
    It was 10 N ^^
    So.. It would look like this: (attachment)
    Therefore, reading = 10N
    Would that be okay?
    Thank you
     
  5. Feb 12, 2016 #4

    BvU

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    I think I agree.
    Just for fun: what would the reading be if the spring balance were turned upside down ?
     
  6. Feb 12, 2016 #5
    20N?
    I'm not very sure though..
     
  7. Feb 12, 2016 #6

    BvU

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    I agree - again :smile: !
    I suppose the only way to be really sure is to do the experiment...
     
  8. Feb 12, 2016 #7
    True :D
    Thank you very much :)
     
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