Electric potential question (check my work)

AI Thread Summary
The discussion centers on calculating the velocity of electrons in a beam directed at a copper sphere and determining the charge required to repel the electrons. The user attempts to solve for velocity using the equation 1/2mv^2 = -qΔV but arrives at an implausibly high speed of 2.19 x 10^33 m/s, which exceeds the speed of light. Participants point out that this result is incorrect and highlight the need for a proper approach to the calculations. The user expresses uncertainty about how to proceed with the second part of the problem regarding the charge on the sphere. Clarification and guidance on both parts of the question are requested.
AnthroMecha
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Homework Statement



A beam of electrons with energy 1.20 keV (per electron) is directed towards a solid copper sphere of radius 1.25cm.
a) Determine the velocity of the electrons in the beam.
b) The beam continues to send electrons into the sphere until it is charged up enough to repel the electrons. What is the charge on the sphere at which it stops further electrons from hitting it?

Homework Equations



1/2mv^2=-qΔV
mass of an electron=9.12X10^-31kg
elementary charge=1.602X10^-19 C

The Attempt at a Solution



Not sure if I'm going part a right:
.5(9.12X10^-31kg)v=(-1.602X10^-19 C)(1.2KeV)

Solving for v (velocity) I get 2.19 X 10^33 m/s

Does this look right?

Not even sure what to do to answer part b.

Any help is appreciated!
 
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Sorry, I have no time to check it fully, but 10^33 if way to much for a speed. It's 10^25 times higher than the speed of light!
 
Innoko said:
Sorry, I have no time to check it fully, but 10^33 if way to much for a speed. It's 10^25 times higher than the speed of light!

Yeah, I knew that answer sounded ridiculous.
 

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