what was the acceleration during the segment labeled "A"?

Answer:
[tex]a = 4 m/s/s[/tex]
Explanation:
As we know that the acceleration of an object is defined as the rate of change in velocity of the object
so we can say it is given as
[tex]a = \frac{dv}{dt}[/tex]
so if we have a graph of velocity and time then rate of change in velocity is given by the slope of v-t graph
so here for segment A slope of the graph is
[tex]a = \frac{v_2 - v_1}{\Delta t}[/tex]
[tex]a = \frac{20 - 0}{5 - 0}[/tex]
[tex]a = 4 m/s/s[/tex]