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Sun's Rotational Kinematics

  1. Oct 21, 2006 #1
    The sun appears to move across the sky, because the earth spins on its axis. To a person standing on the earth, the sun subtends an angle of sun = 9.30 x 10-3 rad (see Conceptual Example 2). How much time (in seconds) does it take for the sun to move a distance equal to its own diameter?

    I know that I probably need convert radians to degrees and find the length of the r first?

    I just don't know where the heck the time factor comes in this rotational kinematics problem. There seems to not be enough information.
  2. jcsd
  3. Oct 22, 2006 #2

    Andrew Mason

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    What is the angular speed of the observer on the earth?

  4. Oct 22, 2006 #3


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    Yes, problems like these can make your head hurt.

    Think of it like this: Imagine a laser beam shining from the surface of the earth into the sky. Due to the rotation of the earth this beam will sweep over the sky. How many radians does the beam cover in one second due to the rotation of the earth?
  5. Nov 8, 2007 #4
    The Sun "goes around the Earth" every 1 day, that is, it rotates [tex]2 \pi[/tex] radians per day.

    Convert this to 'radians per second'. Now you have a speed (in radians/second) and a distance (in radians). You can now find the time.
  6. Nov 6, 2008 #5
    Thank god someone answered this. I've been stuck on the exact same problem from the same text. The question is worded quite poorly.
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