What is the physical significance
What is the physical significance of the slope of the graph for the case of the level air track?
The slope of the graph plotted of velocity v/s time will be equal to the acceleration of the car on the air level track.
The slope of the graph for the case of the level air track is zero, hence there is no acceleration and the car moves across the air track with uniform speed.
Whereas in the case of an elevated air track, the slope value indicates the acceleration acting on the car.
Slope signifies the acceleration of the car.