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Homework Help: Electric field problem.

  1. Jan 5, 2013 #1
    A helium nucleus of mass 4u and consisting of 2 protons are traveling at the speed of 7x10^6 m/s strikes a gold nucleus of mass 197u and 79 protons. by considering only the electrostatic repulsion, what is the closest possible distance of approach between them?

    I was considering to use electric field strength here because there's both protons and electrons and then I would be able to find acceleration and use kinematics maybe?? Not sure if I'm on the right track!
  2. jcsd
  3. Jan 5, 2013 #2


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    I'm quite sure that you are to ignore any effect from the electrons.
  4. Jan 5, 2013 #3
    Because they are talking about nucleus only? but is my way of doing correct?? cause I'm not sure how to approach it!
  5. Jan 5, 2013 #4
    Yes, don't consider electrons, because the question tells you to only look at electrostatic repulsion. Also, the electric force in the field increases and causes the speed to decrease as distance between the nuclei decreases.
  6. Jan 5, 2013 #5
    Will the speed eventually reach zero?
  7. Jan 5, 2013 #6
  8. Jan 5, 2013 #7
    Conservation of energy?
  9. Jan 5, 2013 #8
    As the speed decreases what happens to the kinetic energy.
    Loss of one type of energy equals a gain in another.
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