Solving a problem in physics section 71 point 39 electr

39. An electron that has gained speed under the action of a potential difference of 5 kV falls in the middle between the plates of a flat capacitor parallel to the plates. What is the smallest potential difference you need to apply to the capacitor so that the electron does not fly out of it? The length of the capacitor is 5 cm, the distance between the plates is 1 cm.