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## Homework Statement

What is the Kinetic Energy of an electron that passes undeviated through perpendicular electric and magnetic fields if E = 4.0 kV/m and B = 8.0 mT?

[tex]m_{e} = 9.1 \times 10^{-31} \textup{kg}[/tex]

[tex]q_{e} = 1.6 \times 10^{-19} \textup{C}[/tex]

## Homework Equations

I got stuck doing this problem so can someone please help me solve it?

## The Attempt at a Solution

First what I did was I converted the 4.0 kilovolts to 4000 volts and changed to equivalent units - N/C. Then, I used the equation - [tex]\textup{E}= \frac{F}{q}[/tex] to figure out the force on the charge from the electrical field. I found that to be [tex]6.4 \times 10^{-16} \textup{N}[/tex]... Then, I tried finding the force from the magnetic field and got stuck because the equation - [tex]B = \frac{F}{qv}[/tex] requires velocity... The velocity wasn't given and I don't know how to figure it out...

## Homework Statement

An electron moves through a region of crossed electric and magnetic fields. The electric field E = 1000 V/m and is directed straight down. The magnetic field B = 0.4 T and is directed to the left. For what velocity V of the electron into the paper will the electric force exactly cancel the magnetic force?

## Homework Equations

Please help me solve this problem because I have no idea where to start.

## The Attempt at a Solution

I don't have an attempt because I don't know where to start solving the problem.

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