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Homework Help: Light Speed

  1. Feb 20, 2008 #1
    The Sun is 1.5 x 10^11 m from the Earth. How long does it take for the Sun's light to reach the Earth?

    Above is the question I have to answer I was thinking....

    300,000,000,000 meters/1.5*10^11....dunno?
     
  2. jcsd
  3. Feb 20, 2008 #2

    chroot

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    Look at the units:

    [itex]1.5 \cdot 10^{11} \,m \cdot \frac{ 1 s }{ 3 \cdot 10^8 \,m }[/itex]

    Note that the meters cancel, leaving you with seconds.

    If you divide it your way, you get:

    [itex]\frac{ 3 \cdot 10^8 \, m }{ 1 s} \cdot \frac{1}{ 1.5 \cdot 10^{11} \,m} [/itex]

    which has units of 1/s. This isn't a unit of time, so it's not what you want.

    - Warren
     
  4. Feb 20, 2008 #3
    so.........
     
  5. Feb 20, 2008 #4

    chroot

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    Yes?

    - Warren
     
  6. Feb 20, 2008 #5
    I need it in minutes not seconds.?
     
  7. Feb 20, 2008 #6
    so the answer is 5 times 10 to the 18?
     
  8. Feb 20, 2008 #7

    Integral

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    No, you may need to review how to multibly and divide exponents.
     
  9. Feb 20, 2008 #8
    so its 500 seconds...
     
  10. Feb 20, 2008 #9

    chroot

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    Yes, that's correct.

    - Warren
     
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