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Homework Help: Binding energy question

  1. Jan 29, 2006 #1
    "Calculate the total KE of the products of the reaction

    13-C (d,n) 14-N if the incoming deuteron (d) has KE = 36.3 MeV"

    I used the Q-value equation which is

    Q = KEn + KEN - KEn - KEd

    but to find the kinetic energy for each particle, velocity is required (which isn't given in the question)

    So, i tried to use E=MC^2 and didn't work out well

    to calculate the total KE of the products (KE of neutron and nitrogen)

    can't i just use E=MC^2?

    please help:confused:

    Last edited: Jan 29, 2006
  2. jcsd
  3. Jan 29, 2006 #2


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    One has to use conservation of total energy, i.e the sum of kinetic and rest energies before = sum of kinetic and rest energies after.

    The Q value is the difference in rest energy (masses). If Q > 0, the released energy is manifest in the kinetic energy of the products.

    If Q < 0, some energy (e.g. kinetic energy of one or both reactants) must be applied.
  4. Jan 29, 2006 #3
    umm okay
    so you're saying that i should use KE before = KE after?
    but the question is how do i find a kinetic energy of Carbon, neutron and nitrogen?
    using E=mc^2?
  5. Jan 29, 2006 #4


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    Try KE (after) = KE (before) + Q or

    KE(final) = KE(initial) + Q

    and one can use classical mechanics for kinetic energy since 36.3 MeV << 1875.6 MeV (rest mass of d).

    If one wants to calculate the specific kinetic energy of the particles, then one must apply conservation of momentum (a vector quantity) in both the x and y or longitudinal and transverse directions taken with respect to the incident velocity of the deuteron. A reasonable assumption would be that the beam of deuterons is impinging upon a fixed (solid) target of C.
    Last edited: Jan 29, 2006
  6. Jan 29, 2006 #5
    what i'm asking is, is KE(before) = 36.3 MeV?

    KE= 0.5 mv^2, but velocity isn't given in the question
  7. Jan 29, 2006 #6
    i still didn't get it
    perhaps this is too complicated question for physics grade 12 IB
    but thanks anyway
  8. Jan 29, 2006 #7


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    You are given the kinetic energy of 36.3 MeV, which is 1/2 mv2.

    You could calculate v = sqrt(2KE/m).

    Try this page and browse the site - http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html
  9. Jan 29, 2006 #8
    i've never heard of this equation v = sqrt(2KE/m)
    but i'll try!
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