Relative Equilibrium of Liquids — Worked Examples

Each problem first checks the physical regime before applying an ideal formula. Translational examples distinguish no-spill, spill, and free-fall limits; rotational examples distinguish fully wetted, spilling, and dry-core conditions.

Horizontally Accelerating Tank without Spillage

An open rectangular tank is 3.00 m3.00\ \text{m} long and 2.00 m2.00\ \text{m} high and initially contains water to depth 1.50 m1.50\ \text{m}. It accelerates horizontally at 2.50 m/s22.50\ \text{m/s}^2. Determine the two end depths, check for spilling, and find the maximum bottom gage pressure.

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Spilled Volume during Horizontal Acceleration

A rectangular tank is 4.00 m4.00\ \text{m} long, 2.00 m2.00\ \text{m} wide, and 2.00 m2.00\ \text{m} high. It initially contains water to depth 1.80 m1.80\ \text{m} and accelerates horizontally at 3.00 m/s23.00\ \text{m/s}^2. Determine the volume spilled after relative equilibrium is reached.

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Tank Accelerating Vertically Upward

A water tank accelerates vertically upward at 3.00 m/s23.00\ \text{m/s}^2. Determine the gage pressure 1.20 m1.20\ \text{m} below its open free surface.

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Tank Accelerating Vertically Downward

A water tank accelerates vertically downward at 6.00 m/s26.00\ \text{m/s}^2. Determine the gage pressure 1.50 m1.50\ \text{m} below its open free surface and identify the free-fall limit.

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Absolute Pressure during Ideal Free Fall

During an idealized free-fall interval, a connected pressure boundary fixes a liquid at 95.0 kPa95.0\ \text{kPa} absolute. The container and liquid accelerate downward at gg, and other effects are neglected. What absolute pressure exists at a point 2.00 m2.00\ \text{m} vertically away within the connected liquid?

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Combined Horizontal and Upward Acceleration

A 5.00 m5.00\ \text{m} long tank accelerates horizontally at 4.00 m/s24.00\ \text{m/s}^2 while accelerating upward at 2.00 m/s22.00\ \text{m/s}^2. Determine the free-surface angle magnitude and end-to-end elevation difference.

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Rotating Open Cylindrical Tank without Spillage

A cylindrical tank is 1.20 m1.20\ \text{m} in diameter and 1.80 m1.80\ \text{m} high and initially contains water to depth 1.20 m1.20\ \text{m}. It rotates at 60.0 rpm60.0\ \text{rpm}. Determine center and wall depths and check for spilling or bottom uncovering.

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Rotational Speed for Incipient Spillage

An open cylindrical tank has radius 0.750 m0.750\ \text{m}, height 1.50 m1.50\ \text{m}, and initial water depth 1.00 m1.00\ \text{m}. Assuming the surface vertex remains above the tank bottom, determine the speed at which the wall first reaches the rim.

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Onset of a Dry Central Region before Spillage

A cylindrical tank has radius 0.500 m0.500\ \text{m}, height 1.00 m1.00\ \text{m}, and initial liquid depth 0.400 m0.400\ \text{m}. Determine the angular speed at which the rotating free-surface vertex just reaches the tank bottom. Verify that the wall is still below the rim at that instant.

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Radial Pressure Difference in a Closed Rotating Tank

A completely filled cylindrical tank of water rotates at 8.00 rad/s8.00\ \text{rad/s}. Determine the pressure increase from the rotation axis to radius 0.500 m0.500\ \text{m} at the same elevation.

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Gage Pressure at a Point in an Open Forced Vortex

Take the free-surface vertex of a rotating open water tank as r=0r=0, z=0z=0, with zz positive upward. At a point r=0.400 mr=0.400\ \text{m} and z=−0.300 mz=-0.300\ \text{m}, the liquid rotates at ω=5.00 rad/s\omega=5.00\ \text{rad/s}. Determine gage pressure.

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Spilled Volume from a Rotating Cylindrical Tank

A cylindrical tank has radius 0.500 m0.500\ \text{m}, height 1.20 m1.20\ \text{m}, and initial water depth 1.00 m1.00\ \text{m}. After rotation and spillage reach relative equilibrium, the free surface is at the rim at the wall and the center-to-wall elevation difference is 0.800 m0.800\ \text{m}. The center remains wetted. Determine the spilled volume.

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