^^^ he makes a VERY good point, conservation of energy, doesn't matter how long the ramp is, only how tall it is. And the longer it is, the more friction there is, so you're better off with a really steep dangerous one.
want to know your takeoff speed?
mgh = 1/2mv^2
the masses cancel out, so it doesn't matter how fat you are.
you need to set up some datum point, say the takeoff height of the jump. At the top of the ramp, you will have entirely potential energy (gh, where g is 9.81m/s^2 (if working in SI units) or 32.2 ft/s^2 (in english units....lame) and h is the difference in height from the top of the ramp to the takeoff.... e.g., if the ramp is 25ft off the ground, and the lip of the jump is 5 feet off the ground, h=20ft.)
Energy is conserved (ignoring friction, which is a bad assumption) so your total energy at any time will be E = gh
set that equal 1/2v^2 , and then solve for v... this will be your velocity (either in m/s or ft/s depending on units) leaving the ramp.
If you want to account for friction, you just have the get the coefficient of kinetic friction (you could probably guess that or find it in a chart depending on the material you're sliding on) and multiply that by the normal force exerted on you by the ramp (your mass*cos@.... where @ is the angle of the ramp) then multiplied by the length of the ramp (this won't be exactly accurate, because the ramp then curves up, but it will close enough for all practicle purposes, otherwise you'd have to set up some funny integral). Once you have the friction force multiplied by the length, this is the work done by the friction. Subtract this from the total energy, and then solve 1/2v^2 the same way.
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Dont worry, its a controlled slide.
