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  1. Dec 26, 2006 #1
    1. The problem statement, all variables and given/known data
    A bridge of length 60 m and mass 51800 kg is supported at each end. A truck of mass 45000 kg is located 26 m from the left end.

    2. Relevant equations
    What is the force on the bridge at the left point of support?

    3. The attempt at a solution

    I know your supposed to use the sum of the forces equals zero. Then the sum of the torques equal zero, but i can't get the right answer!!:eek:
  2. jcsd
  3. Dec 26, 2006 #2
    the reason is because you are trying to set the sum of all forces equal to zero when you don't even know enough forces. Look at torques. Try my suggestion on the other problem.
  4. Dec 26, 2006 #3

    Doc Al

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    Staff: Mentor

    First identify all the forces acting on the bridge. Then show us exactly how you calculated the torques. (What point did you use as your pivot point?)
  5. Dec 26, 2006 #4
    Its all about the choice of axis. You have all you need if you choose the right point
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