Question

A constant speed has a slope of zero on a graph because no acceleration is taking place.

Answer 1

This is not entirely correct.

You haven't defined the axes of the graph, and it IS tru that if you plot speed against time then the line has 0 slope (note - the slope is change in Y/change in X it is the fact that the re is NO change in Y that gives it the 0 slope..)

Answer 2

Mr Nood is correct, I didn't think about changing the axis to velocity versus time.