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Work due to Gravity

  1. Dec 14, 2009 #1
    1. If your are walking down a flight of stairs would the sign of work be negative, positive or zero?



    2. Well work =FCOS Theta Delta X.


    3. SO I think it would be negative. My reasoning is that the normal force of the person walking down a flight of stairs is in the opposite direction of the gravitational force, so the result is negative work. Does this logic sound correct?
     
  2. jcsd
  3. Dec 14, 2009 #2

    PhanthomJay

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    I don't know about the logic, but the question is poorly worded. Are they looking for the work done by you, or the work done by gravity, or the total work done? You've put a different twist on it...solving for the work done by the normal force...which , confusingly, is actually 0 since the normal force doesn't move.
     
  4. Dec 14, 2009 #3
    The question states what is the sign of the work done by gravity not the person, sorry for the confusion.
     
  5. Dec 14, 2009 #4

    PhanthomJay

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    Well then if you are looking for the work done by gravity on the person, the gravity force points down, and the displacement of that force is also down, so the work done by gravity is, to repeat the question, plus minus or zero??!!
     
  6. Dec 14, 2009 #5
    Well if the forces are pointing in the same direction the sign of work would be positive. Because the equation would reduce to w=Fs.
     
  7. Dec 14, 2009 #6

    PhanthomJay

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    Yes, correct. Gravity does positive work in this case, and you do negative work. That's why I don't climb up stairs too often, but I'll climb down a few floors or so once in awhile:wink:
     
  8. Dec 14, 2009 #7
    hehe nice. Thanks for your help. I understand this concept a lot better now!
     
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