I'm no physicist my any means but...

I think it's supposed to be 9.8m/s^2 (meters per second per second).

Also, a human body hitting the ground isn't going to just stop. Why? Because of the very same law you mentioned. You're forgetting about the fact that the kid will be carrying the same horizontal momentum that threw him off the car when it hit the brakes. Ever seen a motorcyclist lowside on a racetrack? They go a-slidin'. Thank goodness for leathers. Furthermore, I'm pretty sure the coefficient of drag of flesh and bone isn't nearly as high as that of the rubber in the cars tires. So provided the car continued to brake (afterall, isn't that why the kid flew off the hood/sunroof?), it should theoretically stop more quickly than the kid tumbling on the road unless it hit a patch of ice or oil that the kid didn't. Just some food for thought.