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Estimate the increase in the density of seawater at a depth of 400 m below the surface. Take the surface density of water as 1030 kg/m³ and the bulk modulus of water as 2 * 10⁹ N/m² (use g = 10 m/s²).

1. About 2.1 * 10⁻² kg/m³
2. About 2.1 kg/m³
3. About 0.21 kg/m³
4. About 21 kg/m³

Correct answer: About 2.1 kg/m³

Solution

The pressure at 400 m is about 4.12e6 Pa; the fractional density rise is P/B, giving an increase of roughly 2.1 kg/m³.

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