Question

The sound of an explosion on the surface of the lake is heard by a boatman 100 m away and a driver 100 m below the point of explosion.
(i) Explain who will hear the sound of explosion first.
(ii) If the sound takes t s to reach the man how much time will it take to reach the driver?
(speed of sound in air = 344 m/s and speed of sound in water = 1533 m/s )

Answer 1

For the boatman above the surface of the water.

Speed of sound in air = 344 m/s
Distance covered = 100 m
Time taken by sound = t sec
Velocity = distance / time

344 = 100 / t
t = 100 / 344
t = 0.29 sec

Now, for the man below the surface of the water.

Speed of sound in water = 1533 m/s
Distance covered = 100 m
Time taken = t

Velocity = distance / time
1533 = 100 / t
t = 100 / 1533
t = 0.06 sec

So, the man under the water hears the sound of the explosion first.