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Standard Base (SI) Trouble

  1. Sep 14, 2010 #1
    1. The problem statement, all variables and given/known data
    Convert the following as full (decimal) numbers with standard (base) SI units:

    86.6 m

    3. The attempt at a solution

    I thought I could just change it to 8.66x10^1 then just add the 10^-3 because of the milli to make it 8.66x10^-2. But I'm wrong so could someone help me?
     
  2. jcsd
  3. Sep 14, 2010 #2

    vela

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    Did you mean 86.6 mm? I ask because 86.6 m is already expressed in meters.
     
  4. Sep 14, 2010 #3
    What do you mean with: 86.6m?
    Do you mean 86.6 meters?
    If so, meters are SI units so you are done..

    (milli is not a unit, it's a prefix of a unit, meaning a thousandth of that unit)
     
  5. Sep 14, 2010 #4
    Sorry for the typo. I meant 86.6mm.
     
  6. Sep 14, 2010 #5

    vela

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    Is this homework where you enter your answers on the computer? If so, what exactly did you type in for your answer?
     
  7. Sep 14, 2010 #6
    it's a sheet of paper. I got this one now though. 86.6/1000 = 0.0866 which is 8.66E-2.
    Except now I'm getting stuck on 45 microVolts. I don't know how to convert this one. What do you convert microVolts into? Volts?
     
  8. Sep 14, 2010 #7
    Yes, Volt is an SI unit.
     
  9. Sep 14, 2010 #8

    vela

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    Which is the same as 8.66x10-2, so why did you say it was wrong initially?
     
  10. Sep 14, 2010 #9
    Ok I got it. My trouble is that I'm not sure what to convert it into. Like if it's mg I have to convert it go grams right? Or if it's pectoseconds I convert it to a minute? If fentometers then just to meters?
     
  11. Sep 14, 2010 #10


    I said it was wrong initially because the way I derived it was wrong.
     
  12. Sep 14, 2010 #11

    vela

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    No, you need to know what the base units are in SI. For mass, it's the kilogram; for length, it's the meter; and for time, it's the second. There's only one unit for each type of quantity, so all times are in terms of the second, not minutes or hours.
    I wouldn't say what you did was wrong, at least based on how I interpret what you did. Multiplying by 10-3 is the same as dividing by 1000. It's perfectly fine to think of it this way:

    86.6 mm = 8.66x101 (10-3 m) = 8.66x10-2 m

    In fact, it's often how I'll convert units rather than using the relatively long-winded way they teach in school.
     
  13. Sep 14, 2010 #12
    Since the SI for time is seconds then, if it's 600 ps (pectoseconds right?) what else is there to convert to?
     
  14. Sep 14, 2010 #13

    vela

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    ps stands for picoseconds. I assume you're supposed to express it in terms of seconds. Just like you converted millimeters to meters in the first problem, you want to convert picoseconds into plain old seconds.
     
  15. Sep 14, 2010 #14
    I'm just getting really frustrated because I keep confusing myself for some reason.

    Thanks for the help though, much appreciated.
     
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