As a starter look at horizontal and 45 degree launch which would give the extremes and then work your way towards the angles at the incident. What sort of 'flight' distance are you looking at? What was the set up of the central reserve and what could have altered to something other than a smooth launch.
How do you know it was launched. Presumably because there are no marks between launch point and landing! what was the max height of an object between launch / land, and how far was it from launch/land - so we can get an indication of its height or drop during flicht. Was it a drop between L/L and if so, by how much. Using a 45 degree launch angle (optimum/minimum)) its about 38mph. Pretty much what ever angle you come up with, there will be someone to debate how the vehicle pitched in flight due to the front tending to be much heavier than the rear. Or that the height of the kerb has little influence on the launch angle - best exampled that many vehicle simply drive up, on and over it, to the extreme the front rears up significantly whilst the rear wheels stay on the ground (exampled by the demos at monster truck shows). For your scenario you may want to look at other means of speed assessment
