How do I calculate the potential energy of a toy pull back car?

For a physics project I'm using a toy pull back car. I need to calculate aspects about it such as speed and energy. From what I understand they contain a spring which allows it to store potential energy and release kinetic energy slowly. I think there might be gears as well. I'd like to know what sort of formulas I could use to calculate energy stored or how far it would travel. Basically how would I calculate things about it?|||Realistically, you can't actually calculate much of anything due to friction and air resistance and such. But for a basic project, it's probably fine to just disregard those factors and use conservation of energy.





E tot = E ' tot





First you need to know the spring constant of the spring, which you can either look up, or calculate yourself as follows:





(1/2)kx^2 = (1/2)mv^2


kx^2 = mv^2


k = [mv^2]/[x^2]





So you'd have to put the car on the ground, pull the spring back some distance x (measure that), let it go a known distance of say 1m and measure the time. Knowing the distance and time you could calculate the velocity and all that's needed would be a mass measurement.





Now you basically have three types of energy you can play around with: kinetic, potential gravitational and potential elastic (ie the spring energy.) So by setting up different situations, you could calculate a fair number of things. For example, you could set up a track (Hot Wheels type thing) with the car at the bottom and determine the maximum height pulling the spring back some distance would take the car:





(1/2)kx^2 = mgh


h = [(1/2)kx^2]/[mg]





Done!|||Kinetic Energy= mv虏 (mass times velocity squared)





Potential Energy + Kinetic Energy + Heat lost to friction = Total energy





What this basically means is that whenever the spring is pulled back fully, all the energy is potential, and none is kinetic. Once the spring is released, the potential energy is being transformed into kinetic energy. Kinetic energy is the energy of movement. Half way through the release, when the car has the most kinetic energy, it has the least potential energy. The total amount of energy is the same, but it is converted from potential to kinetic. However, energy is lost due to friction. Friction causes energy to be converted to heat. At the end, when the car comes to a stop, all energy has been lost to friction and converted to heat.|||Here you go: http://en.wikipedia.org/wiki/Torsion_spr鈥?/a>