# Quick physics question

1. Homework Statement

A uniform electric field of magnitude 678 N/C exists between two parallel plates that are 4.02 cm apart. A proton is released from the positive plate at the same instant that an electron is released from the negative plate. Determine the distance from the positive plate at which the two pass each other. (Ignore the electrical attraction between the proton and electron.)

2. Homework Equations
no relevant questions I can think of.

3. The Attempt at a Solution

Honestly I'm not even sure how to approach this question in terms of acceleration and velocity of these masses due to an electric field. I dont want somebody to do my homework for me, I just need some guidance of what equations to use and how to set them up.

Any help would be appreciated. Thanks!

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mjsd
Homework Helper
several ideas I can think of immediately are (ie. may not be completely reliable):
parallel plates -> uniform field -> constant acceleration while particles are moving. Force and field strength are related in a simple manner (check your text).. with a bit of luck they should meet at the midpoint between the plates(that's only a guess) It remains for you to work out an expression for the field strength as function of distance away from the plates (or would this be an overkill? nice to check anyway....)

the plates are pretty close and the field is uniform so the prof told us that the field strength would not weeken. He also mentioned that midway is not the correct answer...

ranger
Gold Member
Well here is a hint. The acceleration of a particle in an electric field is proportional to the strength of the field and charge (q) of the particle; and inversely proportional to the mass of the particle. I basically gave you a formula in words.

mjsd
Homework Helper
ah yes, forgot about the difference in mass, my apology