Question

10. Dolphins of the open ocean are classified as Type II Odontocetes (toothed whales). These animals use ultrasonic “clicks” with a frequency of about 55 kHz to navigate and find prey.

a) Suppose a dolphin sends out a series of clicks that are reflected back from the bottom of the ocean 75 m below. How much time elapses before the dolphin hears the echoes of the clicks? (The speed of sound in seawater is approximately 1530 m s-1.)

Answer 1

When a dolphin makes a sound, it goes straight to the bottom at 1350 m/s. This takes a time of

$$t=\frac{75}{1350}\text{ s}.$$

Then the sound reflects from the bottom of the sea and goes straight back to the dolphin, which takes the same time. Therefore, the total elapsed time is

$$T=2t=150/1350=0.11\text{ s}.$$