Solving a problem in physics section 72 point 47 electr

47. The flow of electrons flies into the space between the plates of a flat capacitor at an equal distance from them with a speed υox = 5 Mm / s. What is the smallest voltage that needs to be applied to the capacitor so that the electrons do not fly out of it, if the capacitor dimensions are as follows: capacitor length l = 7 cm; the distance between the plates d = 2 cm?