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Homework Help: Numerical quantities help

  1. Sep 3, 2011 #1
    1. The problem statement, all variables and given/known data

    K(max) = (6.63x10^-34 J s)(7.09x10^14s) - 2.17x10^-19J
    solve for kmax

    2. Relevant equations

    none?

    3. The attempt at a solution
    K = (6.63x10^-34 J s)(7.09x10^14 s) - (2.17x10^-19 J)
    K = (6.63)(7.09)(10^-34)(10^14) J s^2 - (2.17x10^-19 J)
    K = (47.0067)(10^-24) J s^2 - (2.17x10^-19 J)
    K = (4.70067x10^-23) J s^2 - (2.17x10^-19 J)
    K = J [ (4.70067x10^-23) s^2 - (2.17x10^-19) ]
    K = J (10^-19) [ (4.70067x10^-4) s^2 - 2.17 ]
     
  2. jcsd
  3. Sep 3, 2011 #2

    vela

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    -34+14 = ? (It's not -24.)
     
  4. Sep 3, 2011 #3
    oh shoot, stupid mistake! haha, thanks for the catch!
     
  5. Sep 3, 2011 #4

    gneill

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    The expression doesn't make sense from the outset: the units being added are not consistent.
    (J*s)*s = J*s2, which is not the same as J alone, so these items cannot be added together meaningfully.

    Perhaps the first item should be (6.63x10-34 J s-1) ?
     
  6. Sep 3, 2011 #5

    vela

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    The first constant is Planck's constant, which does have units of J s. The second quantity is supposed to be a frequency, with units of s-1. Probably just a typo on the OP's part.
     
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