A parallel plate capacitor has a positive plate with a +1.1 nC and a negative pl

Question

A parallel plate capacitor has a positive plate with a +1.1 nC and a negative plate with a -1.1 nC. Both plates have an area of 100 cm2 and the separation of the plate is 40 mm. An electron is shot away from the positive plate directly toward the negatve plate with an initial velocity of 2.0 x 10^7 m/s. The velocity of the eletron as it strikes the negative plate is closest to...

1.2 X 10^7 m/s

1.5 X 10^7 m/s

1.8 X 10^7 m/s

2.1 X 10^7 m/s

The correct answer is B but I do not know how to solve this question!!

Explanation / Answer

capacitance C=e0 A/D=(8.85*10^-12)*0.01/0.04=2.2125*10^-12 F

V=Q/c=(1.1*10^-9)/C=497.175 volt

change in energy=v*charge of electron

0.5*me*(vi^2-vf^2)=497.175*1.6*10^-19

0.5*(9.1*10^-31)*(4*10^14-vf^2)=497.175*1.6*10^-19

4*10^14-vf^2=174.83*10^12

vf=1.5005*10^7 m/sec

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