Answer:
dg= 942m
Explanation:
given the depth of the granite Us dg = 500m
time between the explosion t = 0.99s
the speed of sound in granite is Vg = 6000m/s
First of all calculate the time it takes the sound waves to travel down through the lake
Vw = dw/t1
t1 = dw/Vw
t1 = 500/1480
t1 = 0.338s.
Let dg be the depth of the granite basin, so the time it takes for the sound to travel down through the granite is t2 = dg/6000m/s......equation(1)
So the total time it takes to travel down to the oil surface will be
t1/2 = t1 + t2
t1/2= 0.338 + dg/6000.
since the reflection on the oil does not change the speed of sound, the sound will take travelling upto the surface the same time it takes to reach the oil
so; t = 2 t1/2
t1/2 = t/2 = 0.99s/2 = 0.495
Now insert into the values of t1/2 into the equation (1) and solve for dg;
we get 0.495 = 0.338 + dg/6000
dg = (0.495 - 0.338) x 6000
dg = 942m.