Initial speed of proton between parallel plate=?

[bored2death97]

Homework Statement

So I just wrote my midterm in physics, and I was curious on how to do the last question.

Parallel plates, length 5.5cm,
Distance between them is 0.3 cm
Electric Field (E) is 5.4x10^4

Asking what is the initial speed of a proton going through the parallel plates if it just misses the top plate when it comes out.
Proton enters plates on bottom left, comes out top right, and the path is parabolic almost.
So Initial speed?

I think these were all the values we were given.

Homework Equations

The Attempt at a Solution

Wasn't sure where to start.

 

[haruspex]

I assume the proton starts parallel to the plates.
Isn't this just like a projectile under gravity? There's a uniform field across the path of the proton, so a uniform acceleration in that direction. How long will it take to 'fall' from one plate to the other?