Hi, I was working my way through the practice test booklet that ETS has available for d/l on their website (30 questions with answers and info about the test).

Anyway, I was wondering about question 29 which reads:

A long thin vertical wire has a net positive charge lambda per unit length and current I in the wire. A charged particle moves with speed u in a straight line trajectory parrallel to the wire and at a distance r from the wire. Auume that the only forces on the particle are those that result from the charge on and the current in the wire and that u is much less than c, the speed of light.

29. he particle is later observed to move in a straight line trajectory parrallel to the wire but at a distance 2r from the wire. If the wire carries a current I and the charge per unit length is still lambda, what is the speed of the particle?

I don't really have a good idea of how to approach the problem or why the answer is what it is (u).

In general, I was wondering if there are complete solutions to the GRE sample tests on the web anywhere?

Thanks!