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Hanging bag by a vertical rope

  1. Oct 14, 2012 #1
    1. The problem statement, all variables and given/known data

    A 115kg mail bag hangs by a vertical rope 3.3m long. A postal worker then displaces the bag to a position 2.2m sideways from its original position, always keeping the rope taut.

    As the bag is moved to this position, how much work is done by the rope?
    2. Relevant equations

    W=F*d

    3. The attempt at a solution
    Tx=-Tcos(theta)
    Ty=Tsin(theta)

    W=-Tcos(theta)*d

    T/3.3m =mg/2.5m to get T

    I wanted to know why this is zero. Doesn't the Tension have a negative component in the opposite direction of motion, so the work done will be negative. The answer is zero but I just wanted an explanation on this one. Thanks!
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 14, 2012 #2

    lewando

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    Gold Member

    Wrope = Fropedrope.

    If Wrope = 0 and Frope (tension) is nonzero, what must be true about drope?
     
  4. Oct 14, 2012 #3
    its zero
     
  5. Oct 14, 2012 #4
    ive got it! thanks!!
     
  6. Oct 14, 2012 #5

    lewando

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    Gold Member

    Which it is, due to the length of the rope not changing. All clear?
     
  7. Oct 14, 2012 #6
    Wouldn't it also be correct to say that T is perpendicular to the displacement?
     
  8. Oct 14, 2012 #7

    lewando

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    Gold Member

    No, it is at some angle, but not 90°.
     
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