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## Homework Statement

Two parallel plates are positioned horizontally and when the potential te?difference between the plates is 400 V, a charged particle is suspended freely 10 cm above the lower plate. If the potential difference is suddenly changed to 200 V, how long will it take the particle to reach the lower pla

## Homework Equations

-dV/dr=E

U=qV

V=kq/r

## The Attempt at a Solution

If the difference between Va and Vb=400 V,

1. 400=kq/r

q=4.44 x 10^-9

2. U=qV, V=200

U=8.89 x 10^-7

3. U=KE

Since there's no mass, this is where I got stuck. Honestly, I've looked at this problem several different ways, and I just really don't understand electric potential well enough to know if what I'm doing even makes sense. Any feedback would be appreciated.