How Fast Does an Electron Move Towards a Charged Plane?

[jcpwn2004]

Homework Statement

An electron is released from rest 4m from an infinite plane of positive charge. The plane produces an electric field with a constant magnitude of 100 V/m. How fast is the electron moving when it collides with the plane? Mass of E = 9.11x10^-31kg.

Homework Equations

Not sure... Ui + Ki = Uf + Kf?

The Attempt at a Solution

 

[kkrizka]

You are given the electric field, not the voltage at the point so you can't use conservation of energy. Remember, electric field * charge = force on charge. You can use this to find the force on the electron, and then use one of the kinematics equations so solve for the speed.

 

[jcpwn2004]

You are given the electric field, not the voltage at the point so you can't use conservation of energy. Remember, electric field * charge = force on charge. You can use this to find the force on the electron, and then use one of the kinematics equations so solve for the speed.

Ok so I did F=EfxQ...(100 v/m)(1.6x10-19) = 1.6x10^-13 J. And then F=ma so A = (1.6x10^-17)/(9.11x10-31) = 1.756x10^13 m/s...

I'm lost what to do after that...what kinematic equation should i use?

 

[kkrizka]

The one that involves initial, final velocities, acceleration and displacement. I believe it is
$$V_f^2 = V_i^2 + 2ad$$