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Another Electric Potential Problem

  1. Feb 24, 2009 #1
    1. The problem statement, all variables and given/known data
    A charge of 2.9*10^-6C is held fixed at the origin. A second charge of 2.9*10^-6 C is released from rest at the position (1.15m, 0.550m). And the mass of the second charge is 2.10 g.
    At what distance from the origin does the 2.9*10^-6 charge attain half the speed it will have at infinity?


    2. Relevant equations

    KE (final) = Potential Energy (initial) - PE (final)

    3. The attempt at a solution
    There was a part A to this question where I figured out the speed it had at infinity. For the second part, I tried to just solve for r using the same equation but it doesn't work. Any tips?
     
  2. jcsd
  3. Feb 24, 2009 #2

    LowlyPion

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    At what distance from the origin does it start?

    Now in terms of Potential Energy is concerned when the velocity is 1/2 of the final velocity, then at what radius if you released a charge would it only have 1/2 the previous part's velocity at ∞ ?
     
  4. Feb 24, 2009 #3
    It starts at 0,0.
     
  5. Feb 24, 2009 #4

    LowlyPion

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    Looks to me like it is
     
  6. Feb 24, 2009 #5
    What should I do with that position? Should I add it to the new radius I get?
     
  7. Feb 24, 2009 #6

    LowlyPion

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    Doesn't the initial position determine the initial potential energy?
     
  8. Feb 24, 2009 #7
    Yes it does....I get it now, thank you!
     
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