Question

How is constant velocity indicated on an acceleration-time graph?

Answer 1

A motion described as a constant, positive velocity results in a line of zero slope (a horizontal line has zero slope) when plotted as a velocity-time graph.

Answer 2

"Constant velocity" means that there is no acceleration. Acceleration = 0 .

So its graph is zero at every time. The line on the graph lies on the X-axis.