Sound travels much farther in water than light, and thus, is used for various underwater applications. A sonar signal sent to find the depth of ocean takes 4 s to return. What is the depth of the ocean at that location if the speed of sound in seawater is 1500 m s$^{-1}$? [Pg. No. 203]

The sonar signal takes 4 s to go from the ship to the ocean floor and return back. So, the time taken to reach the ocean floor is half of this:

$$\frac{4}{2} = 2 \text{ s}$$

Depth of ocean,

Depth = Speed × Time

$$= 1500 \times 2 = 3000 \text{ m}$$

Therefore, the depth of the ocean at that location is 3000 m or 3 km.