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A ball rolling HELP PL0XZ

  1. Apr 21, 2009 #1
    FORCES On a bridge

    A bridge, constructed of 11 beams of equal length L
    and negligible mass, supports an object of mass M


    as shown. (Intro 1 figure) Real bridges of this sort have steel rockers at the ends (check one out sometime), these assure that the support forces on the bridge are vertical even when it expands or contracts thermally.

    Throughout this problem, use g for the magnitude of the acceleration due to gravity.

    MFS_st_1_a.jpg


    Find FP , the vertical force that pier P exerts on the left end of the bridge.


    My attempt:
    I know the mass exerts a clockwise torque on the left end
    and that their is also the force of the whole bridge on the bridge due to gravity

    so Fp = Torqueduetomass + the whole weight force /2 (because it's halved? due to theother end of the bridge helping out)
     
    Last edited: Apr 21, 2009
  2. jcsd
  3. Apr 21, 2009 #2

    Doc Al

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    Staff: Mentor

    Looks like you dropped a factor of 2.
     
  4. Apr 21, 2009 #3

    wait can you please explain?

    (mv^2 + 2mv^2/3) /2 is correct?
     
  5. Apr 21, 2009 #4

    Doc Al

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    Staff: Mentor

    Yes, that is correct. (Don't lose that 2 in the denominator.)
     
  6. Apr 21, 2009 #5
    thanks, i've changed the question now this is one i've had ages to do but keep getting it wrong
     
  7. Apr 21, 2009 #6

    Doc Al

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    Staff: Mentor

    Don't go back and change the question. That turns the thread into gibberish.
     
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