| 
 RE: is this physically possible?
 The fly is stoped, in relativity to the car. 
 
Anyway, think of a graph showing the flys speed to go from a certain speed in one direction, to a splating and going the same way as a car, it has to deaccelarate then accelerate in the other dirrection. 
 
If i feel bored i might make a picture 
 |