An ultrasonic ruler, displays the distance between the ruler and an object, such

Question

An ultrasonic ruler, displays the distance between the ruler and an object, such as a wall. The ruler sends out a pulse of ultrasonic sound and measures the time it takes for the pulse to reflect from the object and return. The ruler uses this time, along with a preset value for the speed of sound in air, to determine the distance. Suppose that you use this ruler under water, rather than in air. The actual distance from the ultrasonic ruler to an object is 25.0 m. The adiabatic bulk modulus and density of sea-water are Bad = 2.37

Explanation / Answer

Then if the speed is V then the distance reading is 30.0 * V / 343, since the sound travels further in the same time. I think it's about 900m/s. More Google...

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I was wrong. 1,484 m/s according to wikipedia

- this might be a trick question. It might display nothing if the electronics gets wet :-)

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OK, Hookes Law gives v = sqrt(Bad/) = 1520.6 m/s which is close to the Wikipedia value

I think I got the distance up-side down. If the ruler time the pulse, and it comes back quicker than expected, the ruler will measure short. So 343*30/1520.59 = 6.77 m

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