Finding electric potential difference to stop a electron between 2 plates

1. May 11, 2008

mjolnir80

1. The problem statement, all variables and given/known data

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?

2. Relevant equations
conservation of energy eqations and electromagnetic equations

3. 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

2. May 11, 2008

G01

I get 285V when I work through your numbers. Your doing the problem correctly, but you may have made an error in computing the numbers. Check your calculations for an error.

3. May 12, 2008

mjolnir80

kewl thanks for confirming that