The net amount of energy needed to stop this electron will be equal to this change in kinetic energy because work net equals change in kinetic energy. So this is ½ 'mvf' squared minus ½ 'mvi' squared initial and final velocity is there. And the final velocity being zero since it's gonna be stopping. So that's zero for that term. So here's the work net in this case is negative ½ 'mvi' squared and that's ½ times it's mass of 9.11 times 10 to the negative 31 kilograms times 1.90 times 10 to the 6 meters per second was it's initial velocity and that's squared. This gives us negative ANSWER joules of work needed to stop the electron. It's negative because this force that stops the electron will be opposite in the direction to its initial velocity