OAR Mechanical Comprehension: Fluids Questions and Answers Flashcards

A tank is filled with water to a height of 5 meters. What is the approximate gauge pressure at the bottom of the tank? (Use g = 9.8 m/s²)

Answer: 49,000 Pa

Gauge pressure equals ρgh = 1000 × 9.8 × 5 = 49,000 Pa.

Two identical ships are floating, one in freshwater and one in saltwater. Which ship sits lower in the water?

Answer: The ship in freshwater

Freshwater is less dense than saltwater, so the ship must displace a larger volume to equal its weight, causing it to sit lower.

If the flow rate through a pipe is 12 liters per minute and the cross-sectional area of the pipe is 4 cm², what is the flow velocity?

Answer: 0.5 m/s

12 L/min = 200 cm³/s; dividing by 4 cm² gives 50 cm/s = 0.5 m/s.

A balloon filled with helium rises in air because of which principle?

Answer: Archimedes' principle — the buoyant force exceeds the balloon's weight

The air displaced by the balloon weighs more than the helium-filled balloon, creating a net upward buoyant force per Archimedes' principle.

In a U-tube manometer containing mercury, one side is connected to a pressurized gas line and the other is open to the atmosphere. If the mercury on the gas side is 15 cm lower than the open side, what does this indicate?

Answer: The gas pressure is above atmospheric pressure

The gas pushes the mercury down on its side, meaning the gas pressure exceeds atmospheric pressure by the equivalent of 15 cm of mercury.

What is the primary reason that airplane wings generate lift, as related to fluid dynamics?

Answer: Air moves faster over the curved top surface, creating lower pressure above the wing

The curved upper surface causes air to accelerate, and by Bernoulli's principle, faster-moving air exerts lower pressure, producing net upward lift.