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Running Horses-SOHCAHTOA

  1. Mar 4, 2007 #1
    Running Horses-----SOHCAHTOA

    1. The problem statement, all variables and given/known data
    A herd of wild horses races across the flat, open plains of the Great Basin in central Nevada. If the horses are running at 12.2 m/s at a compass heading of 340 degrees, what is the northward component of their velocity?

    And, what is the westward component of the horses' velocity?
    2. Relevant equations
    SOHCAHTOA


    3. The attempt at a solution
    i tried to draw the triangle/sketch. but it doesnt work out when i plus it into the SOHCAHTOA.
    my diagram had 20 deg, and i had the hypotenuse at 12.2m/s.
    was tht a wrong diagram?
    can someone tell me know to draw the correct diagram?
     
  2. jcsd
  3. Mar 4, 2007 #2
    What direction is 340 degrees?
     
  4. Mar 4, 2007 #3
    well these are Compass heading in degrees: N=0, E=90, S=180, and W=270

    - i think N can also be counted as 360
     
  5. Mar 4, 2007 #4
    The directions you state are not typical. Usually, 0 degrees is due east, 90 degrees is due north etc.
     
  6. Mar 4, 2007 #5

    cristo

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    Did you have the angle 20 from the vertical? If so, that seems the correct diagram to me.

    What do you mean when you say it doesn't work when you try and use SOHCAHTOA?
     
  7. Mar 4, 2007 #6
    Assuming for a moment that you're working on a relatively simple vector problem, the approach you're taking is correct. Don't forget, 0 degrees is due North (magnetic north); orient your triangle accordingly. You're still finding the same two perpendicular components.

    However, if you're using compass headings, and are referring to "northward" as meaning the geographic north, then the problem will become a bit more complicated, as geographic north and magnetic north differ by a bit, which depends on where you're at. For me, in Western NY, magnetic North is actually about 10 degrees west of true North. For central Nevada, magnetic north is actually about 16 degrees East of true North.

    If you want to have some fun with your teacher, you can correct for this with your original 340 degree angle. I doubt that's what the teacher's actually looking for though. Here's a reference for the direction toward North. (I may be misinterpreting this graph.)
    http://www.ssec.honeywell.com/magnetic/datasheets/an203.pdf
     
  8. Mar 4, 2007 #7

    cristo

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    I've never come across this convention, but in this question it is not the case:

    Using the convention that 90 degrees is north, this would ask for the easterly component.

    @junesmrithi: You are correct in taking the north direction as 0 or 360 degrees.
     
  9. Mar 4, 2007 #8
    My bad, i guess. Not the convention I am used to.
    I understand this, but you could say a negative westerly component (and negative northerly as well). That is what confused me after first reading the OP.
     
    Last edited: Mar 4, 2007
  10. Mar 4, 2007 #9
    I still think it'd be fun to see if the teacher gets flustered with, "then why'd you say 'horses in central Nevada' if you didn't want us to correct the heading? Why not simply say, 'what are the North and West components of a vector...' "
     
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