An electric field applies a force of 9.11x10^-16N to an elctron emitted from the cathode-ray tube at essentially zero velocity.If the field force is constant, find the time required for the electron to reach the screen 20cm from the cathode. The mass of an electron is 9.11x10^-31kg. What is the instantaneous speed of the electron 15 nsec after leaving the cathode?