Determine the depth if the sound from the ship returns after 4 seconds.

Let the time during which the sound returned to the ship – Δt = 4 s, V = 1500 m / s – is the approximate speed of sound in water, h is the depth.
Depth is distance, so it can be found using the formula:
h = Vt,
where t is the time during which the sound only reached the bottom of the sea, that is, half of the total time spent on the passage of the sound:
t = Δt / 2.
Then:
h = V * Δt / 2;
h = 1500 * 4/2 = 1500 * 2 = 3000 (m).
Answer: 3000 m.