in first motion diagram the length of velocity vector is increasing this shows that the velocity is increasing in the magnitude with time so this is an accelerated motion in which a uniform acceleration must be in the same direction of velocity must be there.
In second motion diagram the length of velocity vector is decreasing with time which shows the velocity is decreasing me magnitude which shows a constant deceleration and the direction of acceleration must be opposite to that of velocity
Now by observing both motion diagrams we can say that it is acceleration in both cases
