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Finding force exerted if you know tension, mass, and distance

  1. Oct 9, 2013 #1
    1. The problem statement, all variables and given/known data

    Cliff and Will are carrying a uniform 2.0m board of mass 77kg. Will is supporting the board at the end while cliff is 0.6m from the other end as shown in the following figure. Cliff has attached his lunch to his end of the board, and the tension in the string supporting the lunch is 207N. Find the normal forces exerted by Cliff and Will.

    2. Relevant equations

    I can't seem to find an equation or equations to go with this problem. I have the equation for torque which is: meter*mass*9.8 m/s

    3. The attempt at a solution
    I don't know where to begin.... Any help would be greatly appreciated !
     
  2. jcsd
  3. Oct 9, 2013 #2
    A picture to go with the problem.
     

    Attached Files:

  4. Oct 9, 2013 #3

    haruspex

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    For static equilibrium, the forces must add to zero and the moments must add to zero. What are the forces? Assign variables to any forces you don't know the magnitudes of. What directions do the forces act in? What equation can you write to express that the sum of the forces is zero?
    Next, pick a point to take moments about. Find the moment of each force about that point and write an equation expressing the fact that the sum of the moments is zero.
     
  5. Oct 9, 2013 #4
    Okay thanks. My book says the forces should add to 1000N.
     
  6. Oct 9, 2013 #5
    Here is some more notes/info that may help figure this problem out.
     

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  7. Oct 9, 2013 #6
    More notes
     

    Attached Files:

  8. Oct 9, 2013 #7
    And more notes.,
     

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  9. Oct 9, 2013 #8
    Last one..
     

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  10. Oct 9, 2013 #9

    haruspex

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    No, all the forces on the board must add to zero. If not, the board will accelerate.
    The various images you later posted seem to be for other problems.
    Please try to answer the questions in my initial response.
     
  11. Oct 12, 2013 #10
    How do I go about in solving this? Help!!
     
  12. Oct 13, 2013 #11

    haruspex

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    Please try to answer the questions I asked:
    - List all the forces (there are four)
    - What directions do you think they act in?
    - Assign a symbol to each
    - What equations/laws are you aware of that can be used to relate them?
     
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