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Math Help - 3D Force System

  1. #1
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    3D Force System

    Hello all. Im so thankfull to have found this site and hope some one can help me. I have exams coming up and am basically completely stuck on these 3D force systems for some reason I cannot get them through my head.

    Would anyone be able to walk me through these problems?

    Thanks in advance

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  2. #2
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    Quote Originally Posted by monkeybars View Post
    Hello all. Im so thankfull to have found this site and hope some one can help me. I have exams coming up and am basically completely stuck on these 3D force systems for some reason I cannot get them through my head.

    Would anyone be able to walk me through these problems?

    Thanks in advance
    The direction of the force is

    \overrightarrow{AB} = \overrightarrow{OB} - \overrightarrow{OA} = (-4, -4, 2)

    The length of this vector is: |(-4, -4, 2)| = \sqrt{16+16+4} = 6

    The length correspond with magnitude F = 30 kN = k \cdot |(-4, -4, 2)|~\implies~ k = 5 and therefore \vec F = (-20, -20, 10)

    So it is answer b)
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  3. #3
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    Thanks a lot!! Any ideas with the other 3?
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  4. #4
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    Quote Originally Posted by monkeybars View Post
    Thanks a lot!! Any ideas with the other 3?
    to Q13:

    Keep in mind that the x-axis has the direction vector (1,0,0). Then use the formula

    \cos(\alpha) = \frac{(-4,-4,2) \cdot (1,0,0)}{6 \cdot 1}

    to calculate the angle between \vec F and the x-axis.

    The other two angles are calculated similarly. (For your confirmation only: If I didn't make a mistake it is answer a))
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  5. #5
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    Thank u earboth!!
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