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Homework Help: Ranking the Magnitude of forces

  1. Nov 6, 2014 #1
    1. The problem statement, all variables and given/known data

    Rank the magnitude of Fn, Fg and Ff of a suitcase sliding down a slope at a constant speed

    2. Relevant equations
    I'm not really sure about this but im guessing

    3. The attempt at a solution
    So if it's going down the slope at a constant speed then the sum of all forces is 0. so does that mean they're all equal?
  2. jcsd
  3. Nov 6, 2014 #2


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    You should explain what Fn, Fg, Ff are under "relevant equations".

    You are right: In case of constant velocity, their sum is zero. How can the sum of forces equal to zero if all are equal?

    Also recall the forces are vectors. What are the directions of the individual forces Fn, Fg, Ff?
  4. Nov 8, 2014 #3
    i think you mean by Fn: the normal force,Fg: gravititional force: and the Ff is due to friction

    in an italic surface with constant speed the surface component of Fg is equal to Ff and so, the normal component to the surface of Fg is equal to Fn

    so the ranking should depend on the slope of the surface

    if you suppose that the angle of the surface is 0<z<90

    when Z is less than 45 the ranking Fg>Fn>Ff
    when Z is greater than 45 : Fg>Ff>Fn
    when it is equal to 45 : Fg>Ff=Fn
  5. Nov 8, 2014 #4


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    Please do not post solutions (except as alternative methods after a solution has already been posted by the thread originator). On homework forums, you should only post hints and point out mistakes.
  6. Nov 9, 2014 #5

    I am really sorry i didn't know that before.

    i promise it will be the last. Thanks
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