Forced, Damped Oscillations

Hi people. Here's the file: http://www.mth.uct.ac.za/Courses/MAM...roject1_07.pdf

Question 1(a) is the one I have a problem with. I just don't know what he's getting at. Is y(x) the function that describes the road? And comparing y(t) and y(x) implies, to me, that x=vt, so it has a constant velocity with respect to the x-axis (in the direction of the x-axis); a very odd thing to do...

Is Y then the vertical displacement of the vehicle from the x-axis? So the car is like a mass on a spring on the road? I have no idea how he derived that Differential Equation.

Any help is much appreciated thanks.

(P.S. I need this pronto please !)