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CollisionsPLEASE HELP

  1. May 27, 2010 #1
    Collisions..PLEASE HELP!!

    1. The problem statement, all variables and given/known data
    (a) A nuclear reactor (see below) contains nuclei that fission when bombarded by slow neutrons. The fission reaction produces fast neutrons which need to be moderated (i.e. slowed down) in collisions before they can cause further fissions. In this problem we consider a reactor which uses graphite (i.e. carbon) as moderator. Assume the neutron and carbon nuclear masses are 1.67 × 10–27 kg and 20.0 × 10–27 kg respectively.

    Consider a head-on collision between a neutron with speed 17.5 Mm/s and a stationary carbon nucleus.


    (i) Calculate the speed of the neutron after the collision

    Mm/s

    (ii) Calculate the speed of the carbon nucleus after the collision

    Mm/s

    (b) An unstable atomic nucleus of mass 17.0 × 10–27 kg which is at rest disintegrates into three particles. One of the particles, of mass 5.00 × 10–27 kg, moves in the y direction with speed 5.90 Mm/s. Another, with mass 8.40 × 10–27 kg, moves in the x direction with speed 2.80 Mm/s .

    (i) Calculate the x component of velocity of the third particle

    Mm/s

    (ii) Calculate the y component of velocity of the third particle

    Mm/s

    (iii) Calculate the kinetic energy released in the process
    fJ


    2. Relevant equations
    do not know.


    3. The attempt at a solution
    i could not make any attempt at this question as it seemed really hard to me, could someone please tel me how to solve all these questions and with formulas? i know its quite alot but my exam is in 2 weeks time and i need to know this one as it very important, thanks!!
     
  2. jcsd
  3. May 27, 2010 #2

    Redbelly98

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    Homework Helper

    Re: Collisions..PLEASE HELP!!

    Here are some general guidelines for this type of problem.
    • Collision problems are usually conservation-of-momentum problems. So use the equation(s) for conservation of momentum.
    • You need to read the wording of each question, or use what you know, to decide if it's a 1-d or 2-d problem.
    • You need to read the wording of each question, or use what you know, to decide if it's an (1)elastic, (2)completely inelastic, or (3)partially inelastic collision. (1) and (2) are common in introductory physics questions, (3) is rare. Another common situation is (4) objects initially together are then moving apart after the "collision".
    • "Head on" means you can treat it as a 1-d problem, since the particles do not rebound at oblique angles.
    Please see if you can come up with the relevant equations and an attempt at a solution from these hints. Check your textbook or class lecture notes for examples if necessary.
     
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