In a cathode$-$ray tube, electrons that start at rest are fired out of a set of plates at a speed of $5\mathrm{.}5{10}^5\frac{m}{s}!$ If the magnitude of the uniform electric field within the plates is $3\mathrm{.}5{10}^4\frac{N}{C},$ how far apart are the plates? $)=(9\mathrm{.}11{10}^{-31}(kg)$