An object moving with constant speed:

The speed of an object is said to be constant if it covers equal distances in equal intervals of time. The distance-time graph as shown in the figure is a straight line.

Its slope gives the speed of the object.

Consider two points A and B on the graph.

Speed of the objects = slope of line AB=  $\frac{Distance \: EF}{Time\: CD}  =\frac{20m}{10s} =2 \frac{2m}{s}$

The speed found in the graph is 2 ms^-1