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Homework Help: Is my teacher wrong? Problem dealing with forces.

  1. Jan 14, 2012 #1
    1. The problem statement, all variables and given/known data
    Problem is in the picture


    2. Relevant equations
    The teacher told us the
    Fnetx = 20N - Fx (Fx is 0)
    Fnety = Fy - 50N (Fy = +25N)


    3. The attempt at a solution
    My answer was 32N. But my teacher said the answer was C. which was 77.5N. He got it because Fnety = 75N for him. But that to me doesn't make sense since the Fy and 50N are pointing in opposite directions, won't Fnety be = -25N?
     

    Attached Files:

  2. jcsd
  3. Jan 14, 2012 #2
    Oh nvm i think i got it. I think he meant to put that:
    25N = Fy - 50 huh? Darn and to think i could prove a teacher wrong ;"D
     
  4. Jan 15, 2012 #3

    Redbelly98

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    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to PF.
    Glad it worked out finally. The key here was to think carefully about which sign (+ or -) goes with each force -- including Fnety, which we know is + because the object accelerates in the +y direction.
    It pays to be careful -- those forces in parentheses should read (Fnetx is 0) and (Fnety = +25N)
     
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