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Math Help - Vector problem

  1. #1
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    Vector problem

    A force of 36N pulls at an angle of 20 degrees above due east. Pulling in the opposite direction is a force of 48N acting at an angle of 42 degrees below due west. Find the magnitude and direction of the resultant force.

    To start off, should I add or subtract the vectors?
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  2. #2
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    Re: Vector problem

    Yes.

    One may wish to break the forces into their orthogonal projections. (North-South and East-West) It should be relatively obvious from there.
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  3. #3
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    Re: Vector problem

    Here is a crude diagram that I made of the problem:



    Is this correct?
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  4. #4
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    Re: Vector problem

    And I meant -42 degrees.
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  5. #5
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    Re: Vector problem

    No good. Go 42 south of west, not 42 west of north.
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  6. #6
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    Re: Vector problem

    42 degrees south of west is -42 degrees, no?
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  7. #7
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    Re: Vector problem

    No, that's 42 West of North. Start at Due West, which is already -90. You need -132 = -90-42.
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  8. #8
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    Re: Vector problem

    Now I'm confused. I thought 42 degrees west (left) of north would be 132 degrees because it would be 90 + 42.
    And if I started at the negative x-axis (or "due west"), wouldn't I be making a 180 degree angle? If I were making a 270 degree angle, I would be starting at the negative y-axis.
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  9. #9
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    Re: Vector problem

    Ahh nevermind, sorry. I should have looked up what due west and due east meant.....
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  10. #10
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    Re: Vector problem

    These definitions are normally included in what we like to call "General Knowledge". :-)
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  11. #11
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    Re: Vector problem

    Pff. If you say so. I just don't get why North is 0 degrees, when on a grid that would be East.
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  12. #12
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    Re: Vector problem

    Yup. Something you do have to get used to. It's just a convention. There are other interesting conventions you will encounter from time to time.
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