I'm doing some MCAT practice, and one question asks: A submarine sends a sonar signal in a direction directly downward. It takes 2.3 seconds for the sound wave to travel from the submarine to the ocean bottom and back to the submarine. How high up from the ocean floor is the submarine? (The speed of sound in water is 1489 m/s). The answer turned out to be about 1700 m, using simple speed x time to give 3400, and then dividing by 2. Why exactly is gravity not a factor in this problem?