A stationary observer notices that the average wave speed for a group of waves is 4 m/s.

If the distance between each crest is 0.02 km, how long does it take for each wave crest to

pass the observer?

Each crest takes 5 seconds to pass the observer

Step-by-step explanation:

First, we need to convert all the units to be the same.

Speed is given in meters per second and length in kilometers, so we will convert kilometers to meters:

One kilometer has 1000 meters, so that means that 0.02 km has 20 meters.

Now, we can solve the problem:

speed equals to length over time, or in equation v = s/t

That means that t = s/v

t = 20m / 4 m/s

t = 5 s