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: Hydrogen atom

  1. Apr 11, 2006 #1
    Hey everyone,
    I have a practice problem that I can't figure out:

    A hydrogen atom is initially at rest and in the n=2 state. Subsequently, it decays to the ground state by emitting a photon. What is the speed of the recoiling atom afterwards? (Mass of H atom = 1.67 * 10^-27 kg)

    My approach is to find the difference in energy between the two states by using E = -13.6/n^2 for each state (n=1 and n=2), then finding the energy difference, and setting that equal to (1/2)mv^2 and solving for v, but I'm not getting the right answer. (The correct answer is 3.4 m/s)
    Can someone help me with this?

    Thanks in advance

    -s
     
  2. jcsd
  3. Apr 11, 2006 #2
    use 4 in work reverse?
     
  4. Apr 11, 2006 #3

    dav2008

    User Avatar
    Gold Member

    I would use conservation of momentum.
     
  5. Apr 12, 2006 #4
    Using conservation of momentum solved the problem, thanks.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook