During a science camp near a lake, a fire-cracker is ignited exactly 1000m from the pier where two students are stationed. Student P is standing on the pier in air, while student Q is scuba-diving just below the water surface at the same horizontal distance.
(i) Compute the time required for the sound of the explosion to reach student P, taking the speed of sound in air to be 340m/s.
(ii) Compute the time required for the sound to reach student Q through water, taking the speed of sound in water to be 1500m/s.
(iii) Find the time difference between the arrivals of the sound for the two students.
(iv) Comment briefly on how this difference might be important for underwater communication during rescue operations.