Question

An athlete swims from the north end to the south end of a 50.0 m
pool in 20.0 s and makes the return trip to the starting position in
22.0 s.

Answer 1

Take southward as the positive direction (or just state directions explicitly).

First leg (north → south):
- Displacement = 50.0 m south, time = 20.0 s
- Average speed = distance/time = 50.0/20.0 = 2.50 m/s
- Average velocity = displacement/time = 50.0/20.0 = 2.50 m/s (south)

Return trip (south → north):
- Displacement = 50.0 m north, time = 22.0 s
- Average speed = 50.0/22.0 = 2.27 m/s
- Average velocity = −50.0/22.0 = −2.27 m/s (i.e., 2.27 m/s north)

Whole round trip:
- Total distance = 100.0 m, total time = 20.0 + 22.0 = 42.0 s
- Average speed = total distance/total time = 100.0/42.0 = 2.38 m/s
- Total displacement = 0 ⇒ average velocity = 0/42.0 = 0 m/s