OAR OAR Mechanical Comprehension: Fluids 2

Question 1

A hydraulic jack uses a small piston of area 2 in² and a large piston of area 20 in². If you apply 50 lbs to the small piston, what force does the large piston exert?

Accepted Answer

500 lbs

Answer

Pascal's Law: Force ratio equals area ratio, so 50 × (20/2) = 500 lbs.

Question 2

Water flows through a horizontal pipe that narrows from 4 in² to 1 in² cross-section. How does the velocity change at the narrow section?

Accepted Answer

Velocity quadruples

Answer

By continuity (A₁v₁ = A₂v₂), if area decreases by factor 4, velocity increases by factor 4.

Question 3

Which of the following best describes gauge pressure?

Accepted Answer

Pressure measured relative to atmospheric pressure

Answer

Gauge pressure is the pressure above (or below) local atmospheric pressure, not referenced to vacuum.

Question 4

A solid steel cube and a hollow steel cube of the same outer dimensions are submerged in water. Which experiences greater buoyant force?

Accepted Answer

Both experience the same buoyant force

Answer

Buoyant force equals the weight of displaced fluid, which depends only on the submerged volume — identical for both cubes.

Question 5

Oil with a specific gravity of 0.85 floats on water. If the oil layer is 10 inches thick, what pressure (in psi) does it add at the oil-water interface? (Water weighs 0.0361 psi/in)

Accepted Answer

0.307 psi

Answer

Pressure = specific gravity × water pressure per inch × depth = 0.85 × 0.0361 × 10 ≈ 0.307 psi.

OAR Test Practice Test

OAR Test Practice Test

OAR OAR Mechanical Comprehension: Fluids 2