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Quick question w = ma

  1. May 13, 2007 #1
    1. The problem statement, all variables and given/known data
    I have to find the mass of something.... the weight is 358170 lbs


    2. Relevant equations

    w = ma
    a = 9.8m/s2
    3. The attempt at a solution
    do i convert lbs into kilograms?
     
  2. jcsd
  3. May 13, 2007 #2

    Hootenanny

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    Edit: Correction, you should convert lbs (force) into newtons.
     
    Last edited: May 13, 2007
  4. May 13, 2007 #3
    so then what would the unit for the mass be
     
  5. May 13, 2007 #4

    Hootenanny

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    See the correction in my previous post.
     
  6. May 13, 2007 #5
    thank you very much
     
  7. May 13, 2007 #6
    Now that i have mass, I need to find the debroglie wavelength...
    so i did wavelength = h/mv

    what unit is used for the debroglie wavelength

    i have J-s/(Kg)*(km/h)

    it should be a distance i believe, so would it be kilometers?
     
    Last edited: May 13, 2007
  8. May 13, 2007 #7

    Hootenanny

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    You need to convert your speed to km/s, then your distance will be in km. However, it is generally best to work in SI units throughout, i.e. m,s, kg etc.

    In general the de Broglie wavelength is usually expressed in nm.
     
  9. May 13, 2007 #8
    why dont you stick to SI units for a while..that would allow easy substitution of h .
    Convert velocity to m/s
     
  10. May 13, 2007 #9
  11. May 13, 2007 #10

    Hootenanny

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    You may want to check your conversion from pounds-force to newtons to kilograms.
     
  12. May 13, 2007 #11
    I used google and it gave me:
    (4 293 203.81 N) / (9.8 (m / (s^2))) = 438 082.021 kilograms
     
  13. May 13, 2007 #12

    Hootenanny

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    Note that pounds-force is not the same as pounds. You need to convert 358170 pounds-force into newtons, then convert this into kg.
     
  14. May 13, 2007 #13
    358170/9.8 = 36547.959N
    = 3 726.854 623 472 kilograms
     
  15. May 13, 2007 #14

    Hootenanny

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    Again, this is not correct. Type into google "convert pounds force to newtons";

    358170 [pounds-force] = 358170 x 4.44822162 [newtons]
     
  16. May 13, 2007 #15
    358 170 pounds force = 1 593 219.54 newtons
     
  17. May 13, 2007 #16

    Hootenanny

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    Correct. Now convert that into kg
     
  18. May 13, 2007 #17
    to Kg = 162573.4224
     
  19. May 13, 2007 #18

    Hootenanny

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    Beware of rounding errors. I get 162407.7
     
  20. May 13, 2007 #19
    1 593 219.54 / 9.8 = 162 573.422
    using google i got this answer
     
  21. May 13, 2007 #20

    Hootenanny

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    Apologies, I was using g = 9.81, your correct. :approve:
     
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