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Homework Help: Find the magnitudes and directions of the forces F1 and F2

  1. Dec 7, 2004 #1
    In a figure a ladder 20 ft. long leans against a vertical frictionless wall And makes an angle of 53 degrees with the horizontal which is a rough surface. The ladder is in equilibrium. Its weight is 80 pounds and its center of gravity is in teh center of the ladder. Find teh magnitudes and directions of teh forces F1 and F2.
  2. jcsd
  3. Dec 8, 2004 #2


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    The question is impossible to answer without knowing what F1 and F2 are. However, analysis of the problem isn't particularly hard. You have a force - the weight of the ladder - pulling straight down on the CoG. There is a normal force from the wall and another from the ground. The end result is that there's a torque on the ladder - if it were to slide down the wall, it would rotate at the base. Pick a pivot point - exactly where doesn't matter, but you'd be wise to put it at the location of one of your unknown forces. Then, do a torque balance on it. Since it is in equlibrium, you know that the net torque must be zero. (This, by the way, is why you put the pivot at the location of an unknown force - since the distance of that force from the pivot is 0, that force cancels out of the equations.) You will probably also have to do a force balance, but that isn't hard - again, the net force is 0. Chances are you'll end up with two equations in two unknowns, the solution to which is simple algebra.

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