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Homework Help: Find A Force

  1. Apr 18, 2010 #1
    While two forces act on it, a particle is to move at the constant velocity v = (3 m/s) - (4 m/s) . One of the forces is F1 = (4 N) + (- 7 N) . What is the other force?

    i know the formula Fnet=ma and i cant use it to find mass in this case how can i find mass first so and i know that velocity is my acceleration here
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 18, 2010 #2

    radou

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    I assume your notation "F1 = (4 N) + (- 7 N)" is a vector component notation? I.e., 4 in the x-direction, and -7 in the y-direction?

    Whatever it is, what does Newton's 2nd law tell you about the not force, if the velocity is constant?
     
  4. Apr 18, 2010 #3
    if it is moving, it continues to move at constant velocity i believe so
     
  5. Apr 18, 2010 #4

    radou

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    Yes, but we know it is moving with a constant velocity. So? What does the sum of the forces equal?
     
  6. Apr 18, 2010 #5
    i guess zero they cancel each other?
     
  7. Apr 18, 2010 #6
    but i need to find a mass in order to find F2, F2 = ma - F1
     
  8. Apr 18, 2010 #7

    radou

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    Why do you think you need the mass? This is only about the forces. Yes, they cancel out. You know one of them. So you can find the other one.
     
  9. Apr 18, 2010 #8
    F2 = ma - F1 using this formula i can find the other force how i am not that great at physics.
     
  10. Apr 18, 2010 #9

    radou

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    Look, F1 + F2 = 0, so F2 = -F1, right? And you are given F1.
     
  11. Apr 18, 2010 #10
    now i understand why cuz when constant velocity acc is 0 and when acc is zero the net force is 0 so F1+F2 =0 is this correct conclusion?
     
  12. Apr 18, 2010 #11

    radou

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    Yes, that is absolutely correct.
     
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