Physics question help?

Question

An athlete swims the length of a 47.0 m pool in 20.0 s and makes the return trip to the starting position in 24.0 s. Determine her average velocities in each of the following below. (Take Δx to be positive when the displacement is in the direction she swims during the first half of the trip.)

(a) the first half of the swim= 2.35 m/s

b) the second half of the swim= -1.96 m/s

c) the round trip

i already figured out a &b but i can't figure out the round trip.

Answer 1

You're asked for the average velocity.  Average velocity is displacement over time.  You know the time - now think about the displacement.  Displacement is a vector, that starts where she started and ends where she ended.  If she made a round trip, then she ended where she started.  So, guess what - displacement is 0!  So her average velocity is 0.  On average, she didn't go anywhere.

Please note that this is different from her average speed.  Her average speed would be her path length over time.  The time is still the same, 44.0 s. Her path length, though, will be 94.0 m.  The difference between the two is largely a result of the difference between the vector velocity and the scalar speed.