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Homework Help: Kinetic energy fusion of protons

  1. Oct 16, 2007 #1
    1. The problem statement, all variables and given/known data
    In a fusion reaction, the nuclei of two atoms join to form a single atom of a different element. In such a reaction, a fraction of the rest energy of the original atoms is converted to kinetic energy of the reaction products. A fusion reaction that occurs in the Sun converts hydrogen to helium. Since electrons are not involved in the reaction, we focus on the nuclei.

    The deuterium nucleus starts out with a kinetic energy of 6.2e-14 joules, and the proton starts out with a kinetic energy of 1.23e-13 joules. The radius of a proton is 0.9e-15 m; assume that if the particles touch, the distance between their centers will be twice that. What will be the total kinetic energy of both particles an instant before they touch?

    What is the kinetic energy of the reaction products (helium nucleus plus photon)?

    C: Gain of kinetic energy:
    What was the gain of kinetic energy in this reaction? (The products have more kinetic energy than the original particles did when they were far apart. How much more?)

    D: Fusion as energy source
    Kinetic energy can be used to drive motors and do other useful things. If a mole of hydrogen and a mole of deuterium underwent this fusion reaction, how much kinetic energy would be generated?
    (For comparison, around 1e6 joules are obtained from burning a mole of gasoline.)

    2. Relevant equations

    Uel = (9E9) (q1q2) / ( r)

    3. The attempt at a solution

    used formula: Uel = (9E9) (q1q2) / ( r)
    as my formula for kinetic energy
    was incorrect

    Last edited: Oct 16, 2007
  2. jcsd
  3. Oct 17, 2007 #2


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    Homework Helper

    Uel = (9E9) (q1q2) / ( r)

    gives potential energy.

    use conservation of energy.

    initial potential energy + initial kinetic energy = final potential energy + final kinetic energy.

    I think you can assume that initial r is infinite... so initial potential energy = 0.
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