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Homework Help: Forces acting on an object

  1. Oct 27, 2013 #1
    1. The problem statement, all variables and given/known data
    An object that is moving at a constant speed velocity is acted upon by three forces. One force is 150 N along the x-axis, the second is 100 N along a direction making a counterclockwise angle of 120° with the x-axis. What is the magnitude of the third force?

    2. Relevant equations
    Not sure, these are the only ones I THINK are remotely relevant (but I have no idea which is why I'm posting here)

    F_x = Fcosθ
    F_y = Fsinθ

    3. The attempt at a solution


    I thought it would just be either 100 N (the same as the northwest force 120° from x-axis) or it would be something involving the Pythagorean Theorem (100^2 + f^2 = 150^2 or 100^2 + 150^2 = 150^2)

    Anyone? This is urgent. My whole class is confused.
    Last edited: Oct 27, 2013
  2. jcsd
  3. Oct 27, 2013 #2


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    Gold Member

    Since it's moving at a constant velocity, what is the sum of the forces on the object?
  4. Oct 27, 2013 #3
  5. Oct 27, 2013 #4


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    Gold Member

    And the x and y directions are independent. So you have two equations, two variables, yeah?
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