[Denman]

right,
if the bee was attached to the bus (ie it was sitting on a seat) then it would go flying into the screen. Like when your in car and you shunt someone you go fowards because you are going at the same speed as the car but dont decelerate as fast as the car.
If the bee was flying around in the bus on its own (as the question states) then it would not go flying into the back as it would be able to decelerate with the same speed, as its momentum isn't high. Its the same in rollercoasters et. If you just brake in a ollercoaster you go fowards b/c the coaster has deceleeated faster than you have (sry my R key is a bit dodgey here lol)