Answer:
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
