A ship at sea sends out simultaneously a wireless signal above the water and a sound signal through the water, the temperature of the water being 4°C. These signals are received by two stations, A and B, 40 km apart, the intervals between the arrival of the two signals being 16.5 s at A and 22 s at B. Find the bearing from A of the ship relative to AB. The velocity of sound in water at to С (ms-1) = 1427 + 3.3t. (Ans: 53.1 °C)
Answers
Answer:The sensation of any sound persists in our ear for about 0.1 seconds. This is known as the persistence of hearing. If the echo is heard within this time interval, the original sound and its echo cannot be distinguished. So the most important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 second after the original sound dies off.
As the speed of sound in water is 1450m/s in the question, the distance traveled by sound in 4 seconds is calculated from the formula
Distance traveled =velocityofsound×timetaken. That is, 1450×4 = 5800 m. This is twice the minimum distance between a source of sound (ship) and the reflector (submarine) as it is reflected sound.
So, the submarine is at a distance of 2900 m or 2.9 km at least from the ship, for the reflected sound or the signal to be heard distinctly.