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Math Help - finding vectors

  1. #1
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    finding vectors

    Hey all,

    needed some help solving two problems presented below.. how do I resolve each one to find Fa using the dimensions as shown..

    sorry missed out the Fa from the bottom B pic..

    hope someone can help. Thanks

    kind regards,
    dadon
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  2. #2
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    sorry I dont think my question was that clear..

    basically it the bottom of the pic the most important for the question using the dimensions as shown above the pictures to find Fa..

    I think you have to subtract or add the vector depending on the way the arrow to get a equation then substitute to find Fa... but not suree
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  3. #3
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    Quote Originally Posted by dadon View Post
    sorry I dont think my question was that clear..

    basically it the bottom of the pic the most important for the question using the dimensions as shown above the pictures to find Fa..

    I think you have to subtract or add the vector depending on the way the arrow to get a equation then substitute to find Fa... but not suree
    The situation isn't clear to me:
    I've modified your drawing A a little bit: Is the line painted in red some kind of lever? Are theose forces in equilibrium? Does the lever rotate about the left end?

    If so:

    The lever is in equilibrium if the sum of the momenti equals zero:

    F_a \cdot 200\ mm - 800\ N \cdot 140\ mm = 0~\implies ~ F_a=\frac{800\ N \cdot 140\ mm}{200\ mm} = 560 \ N
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  4. #4
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    yes thank you

    I checked the answer in the handout and yes it is right!

    do you use the same method for B.
    but not sure with the cosa

    thanks again
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  5. #5
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    Quote Originally Posted by dadon View Post
    ...
    do you use the same method for B.
    but not sure with the cosa

    thanks again
    I've modified your sketch a little bit.

    If you want to calculate the momentum of a force
    - you have to take the component of the force which is acting perpendicular on the lever or
    - you have to reduce the lever to the effective part so the force acts perpendicular to this part.

    I use the second method:

    F_a \cdot 200\ mm\cdot \cos(140^\circ) - 800\ N \cdot 140\ mm\cdot \cos(140^\circ) = 0 ...... Divide the equation by \cos(140^\circ) and you have exactly the same equation as in example A. Thus the result must be in both cases 560 N.
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    Thumbs up

    Thanks earboth for all your help
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