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Cartesian plane distances

  1. Jun 10, 2013 #1
    1. The cartesian coordinates of a point in the xy plane are x=−9.92 m, y=−2.8 m.Find the distance "r" from the point to the origin.Answer in units of m



    2. Relevant equations

    A=sqrt(Axi^2 + Ayj^2)

    3. The attempt at a solution

    i did the following:
    A=sqrt((-9.92m)^2 + (-2.8m)^2) and got for answer 10.30m

    is that right?
     
  2. jcsd
  3. Jun 10, 2013 #2
    also, there's this second part, where I'm stuck.

    Calculate the angle θ between the radius-vector of the point and the positive x axis (measured counterclockwise from the positive x axis, within the limits of −180◦to +180◦). Answer in units of degrees
     
  4. Jun 10, 2013 #3

    lewando

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    Your "r" looks right. Have you tried drawing a picture of the situation?
     
  5. Jun 10, 2013 #4
    for the second one? yes, the point lies in the third quadrant, now the thing is how to get the angle, there's an equation tantheta= y/x, I did it and i got tantheta= .28 which if i want to get the angle,i just have to get tan^-1 right?
     
  6. Jun 10, 2013 #5

    lewando

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    That will give you an angle which will be helpful in determining the answer, but it is not the answer.
     
  7. Jun 10, 2013 #6
    hmmm, okay, then what do you suggest would be the next step then? do I subtract that angle from another one?
     
  8. Jun 10, 2013 #7

    lewando

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    First, what did you get for your arctan(.28)?
    Second, are you clear about how they want you to report the answer "measured counterclockwise from the positive x axis, within the limits of −180◦to +180◦"
     
  9. Jun 10, 2013 #8
    i got 15.64 degrees and no! that part messes me up, i think the limit me, only to the 0 to the 180 (first and second quadrant)
     
  10. Jun 10, 2013 #9

    lewando

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    Is it 0 to 180 (makes no sense)? Or -180 to 180 (makes sense).
     
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