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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...