Oil explorers set off explosives to make loud sounds, then listen for the echoes

Question

Oil explorers set off explosives to make loud sounds, then listen for the echoes from underground oil deposits. Geologists suspect that there is oil under 500-m -deep Lake Physics. It's known that Lake Physics is carved out of a granite basin. Explorers detect a weak echo 0.89 s after exploding dynamite at the lake surface.

If it's really oil, how deep will they have to drill into the granite to reach it? Use values given in (Figure 1) if necessary. (answer is in d_granite)

The speed of sound Medium Air (0C) Air (20°C) Helium (0°C) Ethyl alcohol Water Human tissue (ultrasound Lead Aluminum Granite Diamond Speed (m/s) 331 343 970 1170 1480 1540 1200 5100 6000 12.000

Explanation / Answer

speed of sound in water, v = 1480 m/s

let d is the depth of the lake.

time taken to hear echo, t = total distance travelled/speed of sound

= 2*d/v

==> d = t*v/2

= 0.89*1480/2

= 658.6 m

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