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Homework Help: Vectors help

  1. Apr 16, 2014 #1
    1. The problem statement, all variables and given/known data
    Vector J has a magnitude of 28 ft and a direction of 34 degrees west of north. Vector K has a magnitude of 48 ft and a direction of 20 degrees south of east. Find the magnitude and direction of their sum.
    a) 30 ft and 13 degrees north of east
    b) 36 ft and 54 degrees north of east
    c) 38 ft and 27 degrees south of west
    d) 40 ft and 14 degrees south of west

    2. Relevant equations

    3. The attempt at a solution
    Square root of 28^2 plus 48^2= 55 ft

    34 degrees West of North=304 degrees
    20 degrees south of east=160 degrees
    304 plus 160= 464
    464/2= 232 degrees
    38 degrees west of south
  2. jcsd
  3. Apr 16, 2014 #2
    Hi gurmeet97. Welcome to Physics Forums!!

    Resolve each of the two vectors J and K into x and y components, and then sum the components. This will give you the x and y components of their resultant.

  4. Apr 16, 2014 #3


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    Homework Helper

    It's not clear what convention you are using to measure angles. The standard convention is that east is zero degrees (or 360 degrees after a full circuit) and angles are measured positive counterclockwise, so that north is 90 degrees, west is 180 degrees, and south is 270 degrees.

    You should draw your vectors and the resultant to check your answer. (which isn't one of the choices anyway).
  5. Apr 16, 2014 #4
    Try to break down both vectors in their x and y components.

    "Square root of 28^2 plus 48^2 = 55 ft"
    Wrong, this would only be valid if the vectors were perpendicular to each other.
  6. Apr 16, 2014 #5


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    Gold Member

    My prof used to do that too. 0 is still east, but all your angles aren't necessarily give off the east direction, its just an extra step.
  7. Apr 16, 2014 #6


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    Gold Member

    Oh wait, I see what you mean. I didn't catch ops "solved" directions. It appears as though op is starting west and measuring ccw which will give them -1 of what they want.
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