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Homework Help: Find the De Broglie wavelength

  1. Apr 23, 2007 #1
    1. The problem statement, all variables and given/known data

    Johnny Jumper's favorite trick is to step out of his high-rise window and fall 56.0 m into a pool. A news reporter takes a picture of 70.0 kg Johnny just before he makes a splash, using an exposure time of 7.00 ms. Find the following.

    (a) Johnny's de Broglie wavelength at this moment

    2. Relevant equations

    wavelength = h / (mv) v = x/t

    3. The attempt at a solution

    so I know figured out v which is just 56 m / .007 s = 8000 m/s
    I know m = 70 kg
    I plug it in to the equation wavelength = (6.63e-34) / ((8000)(70)))

    I got 1.18e-39 m. It saids I am wrong, plz help
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 24, 2007 #2


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    Homework Helper

    I'm slightly confused by your first step in which you divide the 56 meter height of the building by the camera's shutter speed to come at 8 thousand meters per second.

    If you are trying to calculate his speed at impact, this is not the right way to do it.
  4. Apr 24, 2007 #3
    You can calculate his speed but using: [tex] v^2=2gs, (u^2=0[/tex] in this case). You can use [tex]\lambda=\frac{h}{\sqrt{2mT}}[/tex] where T is the kinetic energy of the man at that point.

    The virtue of using [tex]v^2[/tex] for this equation is that you can use it directly to calculate the kinetic energy. I think thats it, though I dont know how the shutter speed plays in. The man is accelerating with 'g' at that point if it helps though.
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