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Homework Help: Speed pf the neutron of thorin

  1. Feb 3, 2014 #1
    1. The problem statement, all variables and given/known data
    U → Th + α

    The speed of α = 6 x 105 m/s. Find the speed of neutron of Thorium!

    2. Relevant equations
    E = mc2


    3. The attempt at a solution
    I am pretty sure there is missing information, maybe the mass of α and Th. I just want to ask the way to solve it.

    I thinking using the conservation of momentum. Before U decays, the total momentum is zero, so the total momentum of Th and should be zero. By knowing the mass of Th and α, we can find the speed of Th.

    Is my idea correct?

    And what about the speed of neutron of Thorium? Is it the same as speed of Thorium?

  2. jcsd
  3. Feb 3, 2014 #2


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    I find it hard to believe the wording is "Find the speed of neutron of Thorium". Could you check ?
  4. Feb 3, 2014 #3
    Actually I got it from my friend and he said he was sure that's the exact question

  5. Feb 3, 2014 #4


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    I think Albert E got that right, but if you want to do a momentum balance, that's not a relevant equation!

    Looks good to me. If you write it down nicely, perhaps the masses themselves are not as important as their ratio. Any "missing information, maybe the mass of α and Th" is easily found (decay chain, or: Thorium series).

    And I still can't make head or tail (i.e. can't make sense) out of "speed of neutron of Thorium"
  6. Feb 4, 2014 #5
    Yes, I am just guessing some equations related to the question :shy:

    The equation I think is:
    mTh x vTh = mα x vα

    Yes, the ratio of their masses can be used to solve the equation. I just need to look for the ratio or the mass at the booklet.

    I am also not sure about the speed of neutron, maybe it is speed of Th
    Last edited: Feb 4, 2014
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