Homework Help: A question relating to electricity

1. May 27, 2010

MAHBRAINHURTS

Hi guys, new to the forum so I apologize if I post in the wrong place or something. I'm in an engineering physics II class right now and honestly this material is so hard for me I feel completely overwhelmed (yet sadly I can't get my degree without it). I'm doing some problems right now and have a question on one.

In one problem I'm asked to calculate the speed of a moving electron as it moves towards a charged ring at the point where it reaches the ring, the object is at rest initially and moves towards the ring from some distance. My question with this one is how I take into change in acceleration as it moves closer (if there is an increase in acceleration) to solve it. I guess this is more of a simple kinematics problem, since I can mostly figure out the charge part, but I have a feeling it involves taking an integral of the velocity, and I think I'm making it more complicated than it is.

I might have more questions or find my own solutions so I will edit this thread as needed.

EDIT: I guess this should be moved to the homework forum, sorry. :(

Last edited: May 27, 2010
2. May 27, 2010

Yes, you are right - on two counts. It could be solved by using an integral and some kinematics, and you are making it more complicated than it is. :)

Consider conservation of energy... the initial energy should equal the final energy. The energy contains a velocity term which could presumably be solved for.

Many of these types of physics problems can be solved by kinematics or conservation of energy. When you can, appeal to conservation - its usually easier.

3. Jun 2, 2010

Antiphon

Where does the radiation by the charge fit into the problem? Is it really just simple kinematics?

4. Jun 2, 2010

pgardn

If the electron is initially at rest dont you just need to find the electric potential energy at some distance due to the E field from the ring? This is not a terribly horrible thing. If the electron then reaches the middle of the ring (hopefully), then its all kinetic (no Efield in the very center) and v for the electron can be solved for.

The electron would then move past the ring until it reached the same initial position away from the ring but on the other side, and then return. Or am I making this way too simple?