Final answer:
Jayden can use the concept of echolocation and examples like sonar technology to demonstrate that sound can indeed travel through water and be heard by marine animals like dolphins.
Step-by-step explanation:
Jayden can convince his little brother that sound can be heard through water by explaining echolocation, a process used by dolphins and other animals like bats. He can illustrate that dolphins use sound waves to navigate and find food, emitting ultrasound or sound waves that travel through the water, bounce off objects, and return as echoes. The dolphins process these echoes to understand their surroundings and locate objects, even in complete darkness. This ability is also why they can differentiate between objects underwater, such as discerning two sharks are separate if they are at least 3.50 meters apart based on the echoes received.
He can also mention that sound travels faster in water than in air because water is denser. Jayden could also use examples such as sonar technology employed by submarines, which also relies on the fact that sound travels and is heard through the water to detect objects. This same principle applies to the sound waves Jayden's brother is creating by banging on the side of the boat; they could indeed be heard by dolphins under the water.