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Homework Help: Cylindrical coordinates question

  1. Aug 22, 2012 #1
    1. The problem statement, all variables and given/known data
    https://dl.dropbox.com/u/64325990/cylindrical.PNG [Broken]

    3. The attempt at a solution
    Okay so I found r = 2.24 and z = -3. However I am stuck at finding theta. I think I just don't understand what the question means when it says "In addition, the line defined by theta = 0 in the cylindrical frame points along the y-axis of the Cartesian frame.". I think it means that the new theta = 0 is the y-axis. If that is the case then theta would be greater than 180°/3.14rads. This is obviously wrong; could anyone please explain what is meant by this question?
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Aug 23, 2012 #2


    Staff: Mentor

    compute theta for the standard cyl coords and then subtract pi/4. in xyz a line in the y direction would have a theta of pi/4 but in the problems it should have 0.

    the problem is describing a another cyl coord system different from the one conventionally used to get you to think about what you're doing and what it means to translate points from xyz to another coord system.
  4. Aug 23, 2012 #3
    Okay so I found that the theta for the standard cylindrical coordinates is 5.176. Then if I subtract is by pi/4 I get 4.391. I am still lost :S Don't you mean subtract pi/2? But even then the answer is wrong.
  5. Aug 23, 2012 #4


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    Staff Emeritus
    Science Advisor
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    If θ is measured counter-clockwise in the cylindrical system, then it will be measured clockwise in the Cartesian system.
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