1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calc. Angle between radius vector point and positive x axis? What does that mean?

  1. Jun 7, 2009 #1
    Calc. Angle between radius vector point and positive x axis? What does that mean???

    1. The problem statement, all variables and given/known data

    The cartesian coordinates of a point in the xy
    plane are x = −8.96 m, y = −1.75 m.

    Calculate the angle  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 ◦.

    2. Relevant equations

    arctan of (y/x) = angle/degree



    3. The attempt at a solution

    I did arctan of y/x = 11.051 incorrect....
    I did the arctan of y/x + 180 and got 191.05 incorrect...
    I did that same method - 180 = 168 ish still inccorrect...
    then I did arctan of x/y + 180= 258 ish and still wrong..

    any ideas what this question is asking for? or what the correct answer is??
     
  2. jcsd
  3. Jun 7, 2009 #2
    191.05 looks right but not within the limits of what they want. Try to express that another way.
     
  4. Mar 21, 2010 #3
    I have this exact same problem with different numbers! (UT homework maybe? XD) I'm pretty stuck.
     
  5. Mar 21, 2010 #4

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Read chriscolose's answer. Is 191.05 between -180 and +180?
     
  6. Mar 21, 2010 #5
    Here is my problem:

    The cartesian coordinates of a point in the xy plane are x = −8.83 m, y = −5.47 m. The distance between the point and the origin is 10.38700149. Calculate the angle  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 ◦.

    I have no idea how he got his answer at all.
     
  7. Mar 21, 2010 #6

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    A good start is to draw a picture. What does that tell you?
     
  8. Mar 21, 2010 #7
    Okay, I drew a picture and I have a graph with a circle. I have the radius as 10.38700149 and I drew an arc (representing the angle) from the the positive x axis counterclockwise to the radius in the third quadrant.
     
  9. Mar 21, 2010 #8

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    What trigonometric formulae do you think need to be used to solve this problem?

    Our job here is to help you do your own homework; we do not do your homework for you.
     
  10. Mar 21, 2010 #9
    I understand that. XD That's why I asked. I wasn't expecting anyone to do anything for me. :3

    Anyway, hmm, what formula? I can't say that I know. I mean, I'm thinking it has something to do with sin, but I'm not entirely sure.
     
  11. Mar 21, 2010 #10
    Soh cah toa
     
  12. Mar 21, 2010 #11
    sin=opposite/hyp.
    cos=adjacent/hyp
    tan=opposite/adjacent
     
  13. Mar 21, 2010 #12

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Then maybe your drawing should have a triangle that you can make sense of rather than an arc that you cannot make sense of.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Calc. Angle between radius vector point and positive x axis? What does that mean?
Loading...