OAR Mechanical Comprehension: Fluids Flashcards

A ship displaces 500 tons of seawater. According to Archimedes' principle, the ship's weight is:

Answer: Exactly 500 tons

A floating object displaces fluid equal to its own weight, so the ship weighs exactly 500 tons.

In a venturi meter, the pressure is measured at the wide inlet and the narrow throat. The flow rate is determined from the:

Answer: Pressure difference between inlet and throat

A venturi meter uses the pressure drop between the wide inlet and narrow throat (via Bernoulli's equation) to calculate flow rate.

Which of the following increases the viscosity of most liquids?

Answer: Decreasing temperature

For most liquids, viscosity increases as temperature decreases because molecular cohesion strengthens at lower temperatures.

A hydraulic cylinder with a 3-inch diameter piston must lift 1,000 lbs. What minimum pressure is needed? (Area = πr²)

Answer: About 212 psi

Area = π(1.5)² ≈ 7.07 in²; Pressure = Force/Area = 1000/4.71 ≈ 212 psi using r = 1.5 in correctly.

Laminar flow in a pipe is most likely when:

Answer: The fluid is highly viscous and velocity is low

Laminar flow occurs at low Reynolds numbers, favored by high viscosity, low velocity, and small pipe diameters.

Water hammer in a piping system is caused by:

Answer: Sudden stoppage or reversal of fluid flow creating a pressure shock wave

Water hammer occurs when rapidly closing a valve causes fluid momentum to create a sudden high-pressure shock wave that travels through the pipe.

If the specific gravity of mercury is 13.6, how high a column of mercury corresponds to 14.7 psi (one atmosphere)?

Answer: About 30 inches

Standard atmospheric pressure supports approximately 29.92 inches (≈ 30 in) of mercury, which is why barometers use mercury.