# Finding electric potential difference to stop a electron between 2 plates

## Homework Statement

Question: an electron with a velocity of 5.0x10$$^{}6$$ m/s is injected into a parallel plate apparatus through a hole in the positive plate. it moves across the vacuum between the plates. what would the potential difference have to be in order to stop the electron 25% of the way across the gap?

## Homework Equations

conservation of energy eqations and electromagnetic equations

## The Attempt at a Solution

if we set the base line at the positive plate:
E$$_{}kinetic 1$$ + E$$_{}electric potential 1$$ = E $$_{}electric potential 2$$

Vq + 1/2 mV$$^{}2$$ = Vq(0.75) <---- (to account for the 25%)

V(-1.6 x 10$$^{}-19$$ ) + 1/2 (9.1 x 10$$^{}-31$$ )(5x10$$^{}6$$) $$^{}2$$ = V(-1.6x10$$^{}-19$$)(.75)

when i do this my answer does not come out to what it is supposed to (which is 285 j/c)
what am i doing wrong