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Polar Coordinate Tracking problem

  1. Sep 4, 2011 #1
    1. The problem statement, all variables and given/known data

    You're tracking a plane from the ground. The plane is at a constant height h from the ground, at a distance r from you at the illustrated instant, and at an inclination theta. The plane's speed is constant at 1200km/hr. Find the rate at which your tracking dish must rotate if r=3km and theta=30degrees. Does the acceleration of gravity make any contribution to your answer?

    CCunj.png

    The attempt at a solution

    The correct answer is 0.05 rad/s.

    But this is what I got:

    lZEvz.jpg

    Sorry for the gigantic image!

    Thanks.
     
  2. jcsd
  3. Sep 4, 2011 #2

    vela

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    Check your units.
     
  4. Sep 4, 2011 #3
    461.88 rad/hr = 0.1283 rad/s

    Thanks for pointing that out. Still wrong though :/
     
  5. Sep 5, 2011 #4

    vela

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    You resolved i into er and eθ incorrectly. (Try it with θ=90 degrees, for example.) Also, the r in your expression for V isn't equal to 3 km.
     
  6. Sep 5, 2011 #5
    Why isn't it 3km?
     
  7. Sep 5, 2011 #6

    vela

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    I guess it depends on how you interpret the phrase "distance from you." But if you use r=3000 m, the answer is 0.056 rad/s, which rounds to 0.06 rad/s. If you use 3000 km as the horizontal distance from you, you get 0.048 rad/s, which rounds to the answer you cited.
     
  8. Sep 5, 2011 #7
    Thank you very much. I got 0.06.

    What is the meaning of the second part of the question ("Does the acceleration of gravity make any contribution")?

    Thanks again.
     
  9. Sep 5, 2011 #8

    vela

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    Would you get a different answer if, say, you were on Mars, where the acceleration of gravity is different?
     
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