(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Two stationary positive point charges, charge 1 of magnitude 3.45 nC and charge 2 of magnitude 1.85 nC, are separated by a distance of 50.0 cm. An electron is released from rest at the point midway between the two charges, and it moves along the line connecting the two charges.

What is the speed v(final) of the electron when it is 10.0 cm from charge 1?

2. Relevant equations

Ek= (mv^2)/2

U= (k(q1q2))/r

3. The attempt at a solution

I used the following equation:

Ek(f)+U(f) = Ek(i)+U(i)

(mv(f)^2)/2 + (k(q1q2))/r = (mv(i)^2)/2 + (k(q1q2))/r

(9.1x10^-31)(vf)^2)/2 + (((9x10^9)(3.45nC)(1.6x10^-19))/0.10m) + (9x10^9)(1.85nC)(1.6x10^-19))/0.40m) = (((9x10^9)(3.45nC)(1.6x10^-19))/0.25m) + (9x10^9)(1.85nC)(1.6x10^-19))/0.25m)

(9.1x10^-31)(vf)^2)/2 + 5.6x10^-17 = 3.0 x 10^-17

(9.1x10^-31)(vf)^2)/2 = -2.6 x 10^-17

Then my issue: I end up needing to take the square root of a negative number...yah.

If someone could please point me to the error I've made, it would be appreciated. I'm iffy on my "Ek(f)+U(f) = Ek(i)+U(i)". Did I use the correct equations? Please help, thanks.

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# Homework Help: Speed of an electron in an electric field - trying to find my error.

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