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

  • Thread starter User1247
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1. Homework Statement
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. Homework 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.
 

Answers and Replies

Doc Al
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U=k(q1)(q2)/r=6.912x10^-21J
Redo this, paying attention to the power of ten.
 

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