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Homework Help: Equilibrium at Constant Velocity

  1. Nov 24, 2007 #1
    Hi there. This problem is very basic but I really cannot figure out how to solve it. I'm missing something but I have no clue what it is.

    1. The problem statement, all variables and given/known data
    Three forces act on a moving object. One force has a magnitude of 80.0 N and is directed due north. Another has a magnitude of 60.0 N and is directed due west. What must be the magnitude and direction of the third force, such that the object continues to move with a constant velocity?

    2. Relevant equations
    Force X Y
    F1 F1Cos90 F1Sin90
    F2 -F2Cos90 F2Sin90
    W 0 -W=-mg

    3. The attempt at a solution
    F1Cos90-F2Cos90+0=0 (Then divide by Cos90)


    I would be very thankful if someone could please tell me what I'm doing wrong and what I should be doing so that I may learn from this question.
    Last edited: Nov 24, 2007
  2. jcsd
  3. Nov 24, 2007 #2


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    Science Advisor
    Homework Helper
    Gold Member

    There is no mention of gravity in this problem, so do not try to include it in your solution. Calculate the resultant of the two given forces (magnitude and direction)..one force is along the y axis and the other along the x axis......use pythagorus and basic trig to calculate it. Then what must the third force be to keep the object moving at constant velocity (HINT: Use Newton 1).
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