# Homework Help: Particle kinetic energy

1. Jul 18, 2010

### pat666

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

A particle with charge -3e is accelerated from rest through a potential difference of 200v .
This gives the particle a kinetic energy of????
2. Relevant equations

3. The attempt at a solution
what does a charge of -3e mean???(-3*2.71...???) to kind the KE wouldn't i need a mass too??

2. Jul 18, 2010

### Fightfish

e = charge of an electron.
Try using conservation of energy?

3. Jul 18, 2010

### pat666

ok so the P.d = Ke??
I cant see that - can you give me a bit more please.

4. Jul 18, 2010

### Onamor

when a charged particle passes through a PotDif it "gains energy." (from the fields) since this is a particle of (assumed) no internal structure, the energy it gains will be in kinetic, not potential. Therefore you dont need a mass, the question just wants the energy.

the equation you need is indeed E = q.V (where q is the charge on the particle)

to better understand this, remember that we assume the particle does not "see" the potential when it is at an infinite distance from it (potential **difference** from that at infinity).
So in essence, the value of KinEn is how much the potential "wants" the particle to pass through it.

Last edited: Jul 18, 2010
5. Jul 18, 2010

### pat666

thanks Onamor - problem solved