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Equilibrium problem with a building: I can't figure it out!

  1. Nov 13, 2006 #1
    How should I be going about this problem? Here is the question, diagram, and my work:
    A 50-story building is being planned. It is to be 200m high with a base 40m by 70m. Its total mass will be about 1.8X10^7 kg and its weight therefore about 1.8X10^8 N. Suppose a 200km/h wind exerts a force of 950 N/m^2 over the 70m wide face (fig. 9-73). Calculate the torque about the potential pivot point, the rear edge of the building (Where FE acts in fig. 9-73), and determine whether the building will topple. Assume the total force of the wind acts at the midpoint of the building's face, and that the building is not anchored in bedrock.
    http://img158.imageshack.us/my.php?image=fig973ed8.png Fig 9-73
    -The answer listed in the book is +2.3X10^9, and that it doesn't topple-
    I do not know how to go about this problem, because it asks for the torque yet I am not sure how to get it without messing it up... I tried the torque equation along the x axis and got:
    sum of torque = 0 = -20FEx - 20(66500N(FA))
    so -20FEx = 20(66500)
    or FEx = -66500N
    This is not the torque, I know, but I don't know what to do with this force and am kind of stuck in a rut...
     
  2. jcsd
  3. Nov 13, 2006 #2

    OlderDan

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    Calculate the torque about the lower corner where FE is applied. You know the forces and torques must add to zero if the building is not moving, so you can use any point to calculate the torque, but that lower corner is an easy place to do it.
     
  4. Nov 13, 2006 #3
    ok, I'll try it.
     
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