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Conversion method 2

  1. Sep 15, 2007 #1
    1. The problem statement, all variables and given/known data

    9.8m/s^2= ? in/hr^2

    2. Relevant equations



    3. The attempt at a solution

    (9.8m/s^2)X(1ft/.3048m)=(9.8ft/.3048s^2)=(32.15223097ft/s^2)X(12in/1ft)=(385.8267717in/s^2)
     
  2. jcsd
  3. Sep 15, 2007 #2

    dynamicsolo

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    You're looking good so far. Now take care of the "seconds" in the denominator...
     
  4. Sep 15, 2007 #3
    how to do the seconds

    can i do (385.8267717in/s^2) X (60s^2/1hr^2) = 1388976.378in/hr^2. this answer is not correct
     
  5. Sep 15, 2007 #4

    cristo

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    That's because, firstly, there's not 60 seconds in an hour, and secondly, you need to square this number anyway.

    Think of it like the units are [tex]\frac{in}{s^2}=\frac{in}{s\cdot s}[/tex]. Now, there are 3600 seconds in an hour, so replace that in the denominator to give [tex]\frac{in}{3600^{-2}hr^2}=\frac{3600^2in}{hr^2}[/tex]
     
  6. Sep 15, 2007 #5

    dynamicsolo

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    Cristo is correct. If you aren't fully comfortable with certain conversion factors, you may want to use more steps, as you did correctly with the portion leading from meters to inches:

    (385.8267717in/s^2) X [(60 s/1 min)^2] = (385.8267717in/s^2) X (3600s^2/1 min^2) =

    (385.8267717 in X (3600)/min^2) =

    (385.8267717 in x (3600)/min^2) X [(60 min/1 hr)^2] =

    (385.8267717 in x (3600)/min^2) X (3600 min^2/1 hr^2) =

    (385.8267717 in x (3600) x (3600)/hr^2), and so on to the result. The number will be quite enormous.

    You don't need to try to skip steps when you're not making a familiar calculation: leaving out steps can increase the risk of making a serious mistake.
     
  7. Sep 15, 2007 #6
    i got it. i goofed when i tried being slick and figured 3600s^2 = 60^2/hr^2
     
  8. Sep 15, 2007 #7

    dynamicsolo

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    Everyone does that, including faculty lecturers, who really should know better... It usually ends up saving time (and sometimes embarrassment) to work out more steps when the calculation is unfamiliar, complicated, or subtle, than trying to make leaps in your head...

    Good job!
     
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