There is kinetic energy when it is sitting at the top, then as it goes towards the bottom, the kinetic energy is transformed into potential energy.
The formula for accelerational displacement is at^2/2, so we know that 3.9t^2/2 = 200, or 3.9t^2 = 400. t =

, at = v, so
F=1/(4*pi*e0)*q1*q2/r^2
e0 ≈ 8,854187817·10^−12
F=1/(4*pi* 8,854*10^(-12))*2*10^(-7)*2*10^(-7)/(0,3)^2 H = <span>
0,003995
</span>H ~
0,004
H