Two $2\mathrm{.}0-$cm diameter disks spaced $2\mathrm{.}0$ mm apart form a parallel$-$plate capacitor. The electric

field between the disks is $5\mathrm{.}0105$ V m$.($a$)$ What is the voltage across the capacitor? $($b$)$ An

electron is launched from the negative plate and hits the positive plate with a speed of

$2\mathrm{.}0107$ m s$.$ What was the electron$$s speed as it left the negative plate? $($ans: $1000$ V$,$

$7\mathrm{.}0106$ m s$)$