Question

Examine the graph depicting the transmitted (T) and reflected (R) waves from submarines A and B, which are equipped with a device emitting ultrasonic sounds. Study the graph and answer the following. (Speed of sound in water is 1500 m/s)

1. Name the device used here.
2. Why is ultrasonic sound used in this device?
3. Which submarine is closer to the ship? Calculate the distance of the closest submarine.

Answer 1

(a) The device is SONAR (Sound Navigation and Ranging).

(b) Ultrasonic sound is used because it does not get dissipated easily as it travels through water, allowing the reflected echo to be detected.

(c) Submarine B is closer to the ship because its echo returns in less time. From the graph, the time between transmission and reception is 50 s − 30 s = 20 s. This is the sound’s round-trip time, so the one-way distance is:

\[d = \frac{vt}{2}\]

\[= \frac{1500 \times 20}{2}\]

= 15,000 m

= 15 km

Therefore, submarine B is 15 km from the ship.