Potential difference of falling charge particle

[phymateng]

Homework Statement

A particle of mass 7*10e-5 kg and charge 1e-6 C from point A to point B a distance of 3 m in the Earth's gravitational field. The kinetic energy of the particle decreases by 5.3mJ during this movement. The acceleration of gravity is 9.8 m/s^2. What is the potential difference V_b-V_a?

Homework Equations

I don't know how to get the Electric Field. I know that its a positive charge going in the same direction as the gravitational field. Since the problem says that the final kinetic energy is decreasing, then I know the velocity is decreasing and giving me a hint that there is an electric field counteracting the gravitational field. I could use the sum of all forces to equate both the fields, but that is only when the charge would stop. Do I have the right Idea?

The Attempt at a Solution

Tried to do the sum of all forces and the conservation of energy.

 

[LowlyPion]

W = q*ΔV

So you have Δ½mv² and Δmgh.

So if there was some work involved ... any ideas?