Electric potential question (check my work)

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SUMMARY

The discussion centers on calculating the velocity of electrons in a beam with an energy of 1.20 keV directed towards a copper sphere with a radius of 1.25 cm. The user attempted to apply the equation 1/2mv² = -qΔV, using the mass of an electron (9.12 x 10^-31 kg) and the elementary charge (1.602 x 10^-19 C). The calculated velocity of 2.19 x 10^33 m/s was identified as incorrect, as it exceeds the speed of light by a significant margin. The user also expressed uncertainty regarding the charge on the sphere necessary to repel the electrons.

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Students studying physics, particularly those focusing on electromagnetism and particle dynamics, as well as educators seeking to clarify concepts related to electron behavior in electric fields.

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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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