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Determine the other Force, when given resultant and one force.

  1. Jan 24, 2012 #1
    The question is: The 150lb. force shown is the resultant of two forces, one of which is shown. Determine the other force.

    I cannot figure out how to get the other force. I tried using the parallelogram method and method of components, but have been way off on the answers. The answers on the back of the book says the other Force=87.9lb and θ=3.87°.

    I tried doing the x and y components of each answer but i just end up back with the same numbers i started out with.

    I have tried the pythagoream theorm by subtracting 150 squared from 75 squared which gave me an answer of 130 when rounded, from there I got lost.

    I'm just wondering how to actually determine the other force the correct way. I've been reading the book examples and they only tell you just how to determine the resultant, but not the force, if only one is given.
     

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  2. jcsd
  3. Jan 24, 2012 #2

    PhanthomJay

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    You should find the x and y components of each force F1 and F2, not the x and y components of the given answer.

    Always draw your sketch to a rough scale. Using the graphical method of adding F1 and F2 by placing the tail of F2 on the head of F1 , where the head of F2 coincides with the head of R, will give you a rough estimation of the magnitude. sense, and direction of F2.

    Now note that the sum of the x comp of F1 and F2 is the x comp of R, and the sum of the y comp of F1 and F2 is the y comp of R.

    Welcome to PF!
     
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