Calculating Speed of Charged Particles in Electric Field: An Example"

[StudentofPhysics]

Two particles each have a mass of 5.3 10-3 kg. One has a charge of +5.0 10-6 C, and the other has a charge of -5.0 10-6 C. They are initially held at rest at a distance of 0.75 m apart. Both are then released and accelerate toward each other. How fast is each particle moving when the separation between them is one-half its initial value?


ok, I know:
q1 = +5.0 x 10^-6 C
q2 = -5.0 x 10^-6 C
r = 0.75m
m = 5.3 x 10^-3 kg

Since they are opposite charges they will atract each other.

I can't seem to figure out where to begin on what formula to use to discover the speed without any time.

 

[fargoth]

the fastest way would be transfering the potential energy difference to kinetic energy.

\Delta U=\frac{mv^2}{2}+\frac{mv^2}{2}

if they didn't have the same mass you had to use the momentum conservation eq. aswell.