Open container accelerating vertically upward: effect on pressure at the bottom An open container completely filled with water is moved vertically upward with a uniform linear acceleration. Compared with the static case at rest, how does the pressure at the bottom change?
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Agreater than static pressure
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Bequal to static pressure
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Clesser than static pressure
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Dnone of these
Answer
Correct Answer: greater than static pressure
Explanation
Introduction / Context:Accelerating containers create an apparent body force field in addition to gravity. In vertical accelerations, the hydrostatic pressure distribution is modified by an effective gravity g_eff, impacting bottom pressures and gauge readings.
Given Data / Assumptions:
- Open container, water fully filling the container.
- Uniform upward linear acceleration a.
- Neglect sloshing and compressibility; quasi-static distribution.
Concept / Approach:In a non-inertial frame accelerating upward with acceleration a, the effective body force per unit mass is (g + a) downward. Hence pressure varies as p = rho * (g + a) * h below the free surface (which stays horizontal for uniform acceleration).
Step-by-Step Solution:
Define effective gravity: g_eff = g + a (upward acceleration).Hydrostatic relation becomes dp/dz = rho * g_eff.At the bottom, p_bottom(accel) = rho * (g + a) * H, which exceeds rho * g * H at rest.Verification / Alternative check:Energy viewpoint: additional inertial field increases potential gradient, thus higher pressure at the same depth.
Why Other Options Are Wrong:
- Equal/lesser: contradict the increase in effective gravity.
- None of these: there is a definite, predictable increase.
Common Pitfalls:Confusing upward vs downward acceleration; for downward acceleration, effective gravity is (g − a) and pressure reduces (becoming zero at free fall).
Final Answer:greater than static pressure