I'm looking into making a 2D motocross bike game with plausible physics.
It should look like this:

For a first try, I've created only the player (a motocross driver) and the map (consisting of only straight lines; no curves, to keep it simple).
How should collisions between the motocross bike and the track affect the bike's position and velocity? The bike should rotate if only one of the wheels touches the ground and speed up if the back wheel touches the ground. Pretty standard bike game stuff.
How do I achieve this behaviour?