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Homework Help: Motion in two dimensions

  1. Apr 24, 2010 #1
    1. The problem statement, all variables and given/known data
    Three students push a box. Michael pushes with a force of 200 N at 0 degree. Shannon exerts a force of 150 N at 30 degrees, and Adam pushes with 175 N at 145 degrees. What is the magnitude of the net force?


    2. Relevant equations
    Some trig nothing special

    3. The attempt at a solution
    X Axis
    200+(cos30*150)=329.9N [E]
    cos45*175=123.7N [W]
    329.9-120=209.9N [E]
    Y Axis
    sin30*150=75N [N]
    sin45*175=123.7 [N]
    75+123.7=198.7 [N]

    209.9+198.7= 408.6N
    I am not sure if i did it right at all...i am self taught to any help is appreciated thanks in advance
     
  2. jcsd
  3. Apr 25, 2010 #2
    When splitting the forces into components, you can't simply add the two together. You have to use the Pythagorean theorem.
     
  4. Apr 25, 2010 #3
    kk if i do that i end up with 289N which is still wrong
    im not sure where i went wrong
     
  5. Apr 25, 2010 #4
    Well, at this part "329.9-120=209.9N [E]" I'm not quite sure where the 120 came from. You should be subtracting 175Ncos(180-145). As for the Y axis, at "sin45*175=123.7 [N]", you should be using 35 instead of 45.
     
  6. Apr 25, 2010 #5
    K i don't know why I'm having such difficulty with a question that seemed so easy at first =/
    Here is what i have after your suggestions

    X Axis
    200+(cos30*150)=329.9N (pretty sure you don't round until the end)
    cos35*175= 143N
    329.9-143=186.9
    Y Axis
    sin35*175=100N
    sin30(150)=75N
    100+75=175N
    Hit it with some Pythagorean
    and you get 256N

    Thank you for your help:)
     
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