Answer: 800 kg m -3.
- A 600 kg m<sup>-3</sup>
- B 900 kg m<sup>-3</sup>
- C 800 kg m<sup>-3</sup>
- D 1250 kg m<sup>-3</sup>
Correct answer: C. 800 kg m<sup>-3</sup>
Explanation: Fraction submerged = ρ<sub>block</sub>/ρ<sub>water</sub>, so ρ = 0.8 × 1000 = 800 kg m<sup>-3</sup>.
Since the same volume of fluid must pass every cross-section per second (continuity), the fluid speeds up where the pipe narrows; Bernoulli's equation then says this faster-moving fluid has lower pressure - the principle behind a venturi meter and an aircraft wing's lift.
Concept context
Pressure, buoyancy, Bernoulli equation, viscosity, and surface tension.