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Weight on a Scale Down an Incline vs. True Weight

  1. Mar 6, 2012 #1
    Weight on a Scale Down an Incline vs. True Weight

    1. The problem statement, all variables and given/known data
    Judy fastened a set of bathroom spring scales to a wedge shaped skate board as shown and coasted freely down a 30 degree slope. The wheels were well oiled and the platform supporting the scales was horizontal. What fraction of her true weight was indicated by the scales?
    Why would there need to be a force of friction between Judy and the scales?


    2. Relevant equations
    Fg = mg


    3. The attempt at a solution
    (Pictures in attachments)

    Fg = mg
    Fg_|_ = mgsin60º

    FN = Fg _|_
    FN = mgsin60º

    FNy = FNcos30º
    FNy = mgsin60ºcos30º
    FNy = (3/4)mg

    The weight will be 3/4 the true weight. (I think)


    I'm not too sure why there will have to be friction between Judy and the scale. Will the scale accelerate downwards and she will slip off if there's no friction? Will the scale read zero?
     

    Attached Files:

  2. jcsd
  3. Mar 6, 2012 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your reasoning (and perhaps your trig) is a bit unclear. Try this: What's the acceleration of the woman?
     
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