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

AI Thread Summary
The discussion focuses on calculating the velocity of an electron falling from infinity to a distance of r = 10^-8 m from a charge q1 = 4.8 x 10^-19 C. The potential energy change is calculated using the formula U = k(q1)(q2)/r, resulting in U = 6.912 x 10^-21 J. The kinetic energy is then set equal to the potential energy to find the velocity, leading to v = (2U/m)^(0.5), which gives v = 1.23 x 10^5 m/s. Participants are encouraged to check the calculations, particularly the power of ten in the equations. The discussion aims to clarify any errors in the solution process.
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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?






Homework Equations


U=q1V
V=kq2/r

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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User1247 said:
U=k(q1)(q2)/r=6.912x10^-21J
Redo this, paying attention to the power of ten.
 
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