Chapter 1 - Concepts of Motion - Exercises and Problems - Page 29: 10

The vector are shown in the following diagram:

In (a), there is a net acceleration is in upward direction, and since the initial velocity is in upward direction, there is an increase in magnitude of velocity in upward direction. Thus, the length of velocity vector increases from 2 to 3. In (b), there is a net acceleration is in downward direction, and since the initial velocity is in upward direction, therefore there is a decrease in magnitude of velocity in upward direction. Thus, the length of velocity vector decreases from 2 to 3.