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Forces in Equilibrium - Torque

  1. Nov 6, 2005 #1
    A painter weighing 875N stands on a plank 3.0m long, which is supported
    at each end by a stepladder. The plank weighs 223N. If the man stands 1.0m from one end of the plank, what force is exerted by each stepladder?
    ANSWER: 694.8N ; 403.2N -> (ans provided by my hand-outs)
    Q
    1. how to solve?
    2. does dis have a pivot point pls help...
    Thank you very much 4 helping...
     
  2. jcsd
  3. Nov 6, 2005 #2

    Chi Meson

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    Homework Helper

    1. What have you done so far, or at least what do you think you should do?

    2. Since it is in equilibrium, and NOT rotating, you have the luxury of assigning any point as the pivot point. Choose one of the support points as the pivot.

    PS. Cld u pls use fll wrds? Ths iz not txt mssgng.
     
  4. Nov 6, 2005 #3
    oh sorry


    so how about the weight of the plank & the painter...
    what forces act on it...

    thx
     
  5. Nov 6, 2005 #4

    lightgrav

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    weight of the plank IS one of the forces acting on the system.
    weight of the painter is another.
    are there any more?

    If you imagine this thing starting to rotate, where would it rotate around?
    What are the torques (around that axis) of the Forces you've listed?
     
  6. Nov 7, 2005 #5
    my problem is the two stepladders... how can i find its forces..
    pls give me a hint/formula to use...
    is there any torque acting?
     
    Last edited: Nov 7, 2005
  7. Nov 7, 2005 #6
    There are individual torques but they add up to equal 0, since there is no net rotation. This is an important part of the question.
     
  8. Nov 7, 2005 #7
    So is this an equilibrium problem?
    1. a painter weighing 875N who is 1m from the end of the plank
    2. plank 3.0m which has a weight of 223N
    3. the 2 Ladders which are supporting the plank....

    i cant think of a way or a formula to solve this problem.
    can you help me step by step...plss
     
  9. Nov 7, 2005 #8
    Right, figure out how much downward force he applies, and how much torque he applies about one of the ends of the plank.

    Think about how much downward force the plank applies and how much torque it applies about the same end of the plank as 1.

    You don't need to worry about these. Just notice that because of these two step ladders, the net force on the man-plank system is zero, and also the net torque on the man-plank system is zero..
     
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