# Homework Help: Combining equations.

1. Sep 29, 2010

### Narv

I need to find the velocity of an electron, and the information i have is the Electrical Charge, Mass and voltage difference. The math its self wont be the problem, but combining the two equations below to give the third is driving me nuts.

I need someone to explain how Ek (kinetic energy) could equal ΔEe (change in electrical energy) so they can be combined, or if im totaly wrong, a point in the right direction:

Ek = ½ mv²

ΔEe = QΔV

To give:

v = √2QΔV/m

I was provided the final equation by a friend as a hint, and the only two equations i can find with relevant values are the two above, so I think I'm along the right track. Its just the reason WHY they can be combined that's confusing me.

Thank you.

2. Sep 29, 2010

### rock.freak667

By conservation of energy, the pd used to speed up the electron is converted into KE.

hence QΔV=½ mv2

3. Sep 29, 2010

### Narv

You, Sir, are a wonderful human being, and will have the finest of riches, the most beautiful of women and the highest prestige when I accomplish world domination.

I also owe you a beer.

Thank you very much :)

4. Sep 29, 2010

### rock.freak667

:rofl::rofl: I've never heard that one before!