Practical rail gun question

[farmkid]

A group I am part of is having a Pinewood Derby in a couple of weeks. (See the link if you don't know what a Pinewood Derby is.) Besides the typical rules, we have a division with no rules other than flames aren't allowed (no rockets). People have tried things such as CO2 canisters for propulsion, or contraptions to block other cars. Well, I'm going to give my car a fast start by some sort of propulsion. One idea I have is to basically make my car a rail gun. Here's where I need your help.

Okay, here's the idea: I'll cut the block in half lengthwise (top half/bottom half) and glue a metal plate in the middle to make something of a sandwich. Then, I'll build a starting block of sorts which will sit on the track behind the car with rails extending up either side of the car contacting the metal plate. I will run a current through the rails to propel the car forward. I can get 12 volts and plenty of current easily using my portable jump starter, but anything else will seriously complicate the project. Here's my question: how much voltage/current do I need to get decent, but not excessive (I don't want to kill anyone) acceleration? It has been about 12 years since I studied this in physics and I only remember the concept, not the details of the math.

 

[FrontLine]

Your5 'open' competition doesn't allow flames? Pitty. Next years car I'm going to put a rocket motor in mine. Just a tiny one, but still its going to be spectacular. As for your idea of a rail gun derby variant, wouldnt you need almost half the track to get any decent acceleration?

 

[farmkid]

Apparently they've had people want to try model rocket engines, but rules of the building prohibit open flames. So no, no rockets.

My first idea, and what I suspect I may end up doing anyway, is to drill a hole up into the car from the back for a dowel to go into. A spring around the dowel will propel the car forward when the gate is lowered. That may be easier to do, but the rail gun is much cooler.

As for your idea of a rail gun derby variant, wouldnt you need almost half the track to get any decent acceleration?

I don't know. I only have the length of the car for acceleration to work with, so if I need a much longer length, then I'll go back to the spring idea. The car will weigh somewhere around 1/2 lb, so if I can get 1-5 lbs (~5-25 N) of force, I'll have a very fast car.