Answer:
Zero
Step-by-step explanation:
Average velocity is given by:
![v=(d)/(t)](https://img.qammunity.org/2020/formulas/physics/high-school/jidcwnxn1c0zdocnxtzp97sqgn187ivyra.png)
where
d is the displacement of the trip
t is the time it takes for the trip to complete
In this problem, the net displacement of the swimmer is zero. In fact:
- First, he swims 30.0 m in the north direction
- Then, he travels back (-30.0 m) in the south direction, to the starting position
Since the final position is equal to the starting position, the displacement is zero:
d = 0
And therefore, the average velocity is also zero.