Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: De Broglie Equation Question

  1. Nov 29, 2006 #1
    1. The problem statement, all variables and given/known data
    A bullet of mass 39 g travels at 1060 m/s. Although the bullet is clearly too large to be treated as a matter wave, determine what Eq. 38-13 predicts for the de Broglie wavelength of the bullet at that speed?

    2. Relevant equations
    de Broglie equation: wavelength = h / p where h is Planck constant and p is the particle's momentum magnitude.

    3. The attempt at a solution
    p=sqrt(2*m*K) where K=1/2mv^2. I solved K first and got 21,910,200. Then I solved p and got 41,340. Then I solved for wavelength using the de Broglie eq'n and got 1.604 x 10^-38, but this is not the correct answer. Where did I go wrong?? :grumpy: Thanks for your help!
  2. jcsd
  3. Nov 29, 2006 #2
    Huh, I'd start by solving for the momentum (3.9 * 10^-2 kg)(1.060 * 10^3 m/s) = 4.134 *10 kg*m/s, then I would recall that p = h/wavelength and solve for the wavelength. It should be a really big number (of the order 10^34 in the mks system).

    Good luck.
  4. Nov 29, 2006 #3


    User Avatar
    Science Advisor
    Homework Helper

    It's 39 grams, not kilograms.

  5. Nov 29, 2006 #4
    Yeah, hence it becomes 3.9 times 10^-2 kilograms.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook