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A charge falls from infinity to within r of another charge, find velocity.

  1. Mar 13, 2008 #1
    1. The problem statement, all variables and given/known data
    Velocity of an electron that falls to r from infinity?
    An electron falls from infinity to r=10^-8m from a charge q1=4.8x10^-19C. What is the velocity of the electron?






    2. Relevant equations
    U=q1V
    V=kq2/r

    3. The attempt at a solution
    Potential energy change U. coulomb's constant k=9x10^-9, electron charge q2=1.602x10^-19C, electron mass m=9.11x10^-31kg, kinetic energy Ek=½mv²

    U=k(q1)(q2)/r=6.912x10^-21J
    set U=Ek => v=(2U/m)^0.5=1.23x10^5m/s

    Anyone see where I went wrong? Thanks.
     
  2. jcsd
  3. Mar 13, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Redo this, paying attention to the power of ten.
     
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