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Need help drawing a FBD

  1. Jan 21, 2013 #1
    1. The problem statement, all variables and given/known data

    A superhero and his sidekick are hanging motionless from a rope.
    The superhero’s mass is 90.0kg, while the sidekick’s mass is


    2. Relevant equations



    3. The attempt at a solution

    i tried drawing it out, but not sure
    so I divided the rope into two points, one on the superhero and the other on the sidekick
    and i'm not sure where tension is acting..

    Figure_04_06_08.jpg

    I would say Tension that the superhero has on the rope is acting upwards..I actually dunno..VERY VERY CONFUSING
     
  2. jcsd
  3. Jan 21, 2013 #2

    ehild

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    The two pieces of the rope have different tensions. Tension acts at both ends, with opposite signs. The piece below acts downward to superhero, and the piece above him acts upward.

    ehild
     
  4. Jan 21, 2013 #3
    does the rope exert the tension or the superhero exert the tension?
    when i draw the FBD, where does the point start? with reference to the centre of mass of each person or the rope? thanks
     
  5. Jan 22, 2013 #4

    ehild

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    Do you know Newton's third Law? :smile: The rope acts at the man with its tension. The man exerts force on the rope.

    You can consider both men as point masses (a bit big points :tongue2:), all mass compressed in the CM. When drawing the forces acting on a man, you can draw the arrows starting at the CM, but it is also correct and more clear if you draw one arrow at the foot and the other at the hands.


    ehild
     
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