Eletricity, question from Brazil

[Aldo Gondim]

Hello, I'm with a doubt, and my teacher don't know how to solve, I translated this question to English so it can have some mistakes, please help me!

Homework Statement

(ITA) In a laboratory experiment, electrons are emitted by a metal filament F with virtually no initial velocity and are accelerated through the region I by a potential difference U1 25 × 10 ³ V, applied between F and the perforated plate P. They emerge from the hole of the plate with horizontal velocity and penetrate the region II, where they are forced to cross the uniform electric field of a capacitor whose plates are 5.0 cm long and are separated by a distance d = 0.50 cm as shown. What is the maximum value of U2 ddp between the plates of the capacitor that still allows some electrons reach the region III, where there is electric field?
Is given the figure:
http://img16.imageshack.us/img16/9923/fisita.jpg
Answer = 10 V ³

Homework Equations

How can I find the tension? Using T=q.U

The Attempt at a Solution

Trying to decompound the vectors but didn't work

Thanks

 

[jbsteele]

for any help!If the potential difference between the metal filament F and the perforated plate P is U1 = 25 × 10³ V, then the electric field in region I must be E1 = U1/d where d is the distance between F and P. Since the electrons emerge from the hole of the plate with a horizontal velocity, the electric field in region II must be perpendicular to the direction of the electron motion. The maximum value of U2 (the potential difference between the plates of the capacitor) that allows some electrons to reach region III is given by the equation U2 = E1d, where E1 is the electric field in region I and d is the distance between the plates of the capacitor. Therefore, the maximum value of U2 is U2 = 25 × 10³ V x (0.50 cm) = 10 V³.