acceleration voltage Va
plate voltage Vp

$E=\frac {V_{\text p}}{\text d}=$ ${0}$ $\frac {\text V}{\text m}$

schematic diagram:

Schematic layout of the experiment
Real experiment about deflection of electrons in electric field of a plate capacitor
y(x) =

Replace in $y(x)=\frac{a_{\text{y}}}{2\cdot{v_{0}}^2}\cdot x^2$ the term ${a_y}$ for the acceleration in y-direction with a term, that depands on $V_{\text{p}}$, which can be modified in the experiment.

acceleration in y-direction
$a_y(t)=\frac{F}{m}=\frac{V_{\text p}\cdot e}{\text{d}\cdot m}$