I see, thanks!
Having thought about that, I've learned it this way:
Combining electrical field strength, Efs = Voltage / distance
and Efs = Force / charge
Force . distance = Voltage . charge
Work done by the particle accelerator = Voltage . charge
The work done by the accelerator is...
I've taken a screen shot of the question
[PLAIN]http://img803.imageshack.us/img803/753/73615252.png
I know the answer (I've given it in the spoiler below), I don't understand why that is the answer
Thanks if you can help :)