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

by User1247
Tags: charge, falls, infinity, velocity
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User1247
#1
Mar13-08, 02:41 PM
P: 17
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.
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Doc Al
#2
Mar13-08, 03:40 PM
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Quote Quote by User1247 View Post
U=k(q1)(q2)/r=6.912x10^-21J
Redo this, paying attention to the power of ten.


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