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Homework Help: Kinetic energy of nucleus

  1. May 30, 2005 #1
    A 232 Th (thorium) nucleus at rest decays to a 228 Ra (radon) nucleus with the emission of an alpha particle. The total kinetic energy of the decay fragments is 6.54 x 10^-3 J. An alpha particle has 1.76% of the mass of a 228 Ra nucleus.

    a) Calculate the kinetic energy of the recoiling 228 Ra nucleus.

    b) Calculate the kinetic energy of the alpha particle.

    ** Here again I would use the formula k_f = 0.5(m_1 + m_2)v_(partical)^2 now I know we don't have any velocities to work with but the problem gives me the total kinetic energy = 6.54*10^-3 Therefore I should solve maybe for velocities first in order to plug in and get the kinetic energy of Ra and do the same for the alpha particle. Assuming m_1 = 228 and the alpha particle m_2 = 4.0 I need help seeing if I'm going on the right track with finding the velocities of the particles or is that not necessary ?
     
  2. jcsd
  3. May 30, 2005 #2

    Doc Al

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    Staff: Mentor

    Hint: The speeds of the two fragments can be related using conservation of momentum.
     
  4. May 30, 2005 #3

    Doc Al

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    Staff: Mentor

    Again, that equation would apply if the fragments remained together, but they don't!
     
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