= Solution
By symmetry, the two grounded plates take equal induced surface charge and the <electric field> has magnitude $\sigma/(2\epsilon_0)$ between either plate and the sheet. The <grounded-plate potential of a central charged sheet> is therefore
$$
V_{\rm sheet}=\frac{\sigma d}{4\epsilon_0}\simeq282\,\mathrm V.
$$
An <electron> released at zero potential gains <kinetic energy> $eV_{\rm sheet}$. Thus
$$
\boxed{v=\sqrt{\frac{e\sigma d}{2\epsilon_0m_e}}\simeq9.97\times10^6\,\mathrm{m\,s^{-1}}.}
$$
The planar infinite-sheet approximation neglects edge effects. Here $e>0$ denotes charge magnitude; the electron's negative charge makes it accelerate toward the positive sheet. Relativistic corrections are below0.1%. Numerical constants use rounded CODATA values, not a claim about the historical handbook: $\epsilon_0=8.85419\times10^{-12}\,\mathrm{F\,m^{-1}}$, $e=1.602176634\times10^{-19}\,\mathrm C$ and $m_e=9.10938\times10^{-31}\,\mathrm{kg}$. <CODATA recommended values of the fundamental physical constants: 2022 by National Institute of Standards and Technology>[Vacuum permittivity, elementary charge and electron mass]{ref}
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