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Homework Help: Inclined plane + Inclined force. Normal reaction force = ?

  1. Nov 11, 2008 #1
    ok i'm desperate now lol n this is my first time on PF.

    I've just had an exam and I'm sure i got this question wrong. But i'd like to know:

    the normal reaction force and the tension/Force F.

    The question is: There is this object that has a weight of 20N. It is on an inclined plane that is 30 degrees and it is held by a force 30 degrees to the plane. Determine the normal reaction force and the tension in the string.

    Please give me as much relevant working as possible. Thank you for your help!

    I have attached the diagram/question.

    Attached Files:

    Last edited: Nov 11, 2008
  2. jcsd
  3. Nov 12, 2008 #2

    Doc Al

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    Staff: Mentor

    Show us what you've done and where you got stuck.

    Hint: What are the conditions for equilibrium?
  4. Nov 12, 2008 #3

    Resolving forces, I've figured that the tension/Force F = (20/3)*sqrt3 Newtons

    now....i'm not sure wat the normal reaction force is. My friends are telling me that it's Normal Reaction + Tension - Weight Force = 0...but wat's the weight force then. lol

    The only logic that i can conclude from this is that:
    Normal Reaction force + all vertical components above plane = sum of all vertical components under plane, which kinda makes sense to me n is getting me the right answers right now.

    well looking forward to ur reply =]
  5. Nov 12, 2008 #4

    Doc Al

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    Staff: Mentor

    Good! The way you solved for this was to add up all horizontal force components (parallel to the plane) and set them equal to zero. Do the same for vertical force components (perpendicular to the plane) to find the normal force.

    That's true, but you need to use the vertical components of those forces.

    Sounds good to me.
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