# Homework Help: Distance an electron traveled

1. Nov 6, 2012

### Zarrey

1. The problem statement, all variables and given/known data
A very long, thin straight line of charge has a constant charge density of 2.0 pC/cm. An electron is initially 1.0 cm from the line and moving away ( that is, perpendicular to the line ) with a speed of 1000 km/s. How far does the electron go before it comes back?

i cant seem to find the required equations in my textbook. any help would be great.

2. Nov 6, 2012

### tiny-tim

Hi Zarrey!
Use conservation of energy.

(same for your other thread)

3. Nov 6, 2012

### Zarrey

wow lol. i cant believe i didnt know that. thank you for reminding me :D

4. Nov 6, 2012

### Zarrey

Conservation of energy is different when dealing with electrons it seems. is mass relevent?

5. Nov 6, 2012

### nasu

First, you need to find the field around the line of charge as a function of distance. Gauss' theorem wil do nicely do to the symmetry.
Then you can use the work-energy theorem.

6. Nov 7, 2012

### tiny-tim

no
mass always comes into the KE formula

mass is also relevant if it comes into the PE formula

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