Physics · Fluid Mechanics

JEE Advanced 2021 — Paper 1 — Question 8

A cylindrical tube, with its base as shown in the figure, is filled with water. It is moving down with a constant acceleration aa

along a fixed inclined plane with angle θ=45∘.P1\theta=45^{\circ} . \mathrm{P}_{1} and P2\mathrm{P}_{2} are pressures at points 1 and 2 ,

respectively located at the base of the tube. Let β=(P1−P2)/(ρgd)\beta=\left(P_{1}-P_{2}\right) /(\rho g d), where ρ\rho is density of water, dd

is the inner diameter of the tube and gg is the acceleration due to gravity. Which of the following statement(s) is(are) correct?

Question figure
  1. Option A:

    β=0\beta=0 when a=g/2a=g / \sqrt{2}

    Correct
  2. Option B:

    β>0\beta>0 when a=g/2a=g / \sqrt{2}

  3. Option C:

    β=2−12\beta=\frac{\sqrt{2}-1}{\sqrt{2}} when a=g/2a=g / 2

    Correct
  4. Option D:

    β=12\beta=\frac{1}{\sqrt{2}} when a=g/2\mathrm{a}=\mathrm{g} / 2

Answer: A, C

Step-by-step solution

(P1−P2)ds=ρdsd2( gsin⁡45−a)\left(\mathrm{P}_{1}-\mathrm{P}_{2}\right) \mathrm{ds}=\rho d s d \sqrt{2}(\mathrm{~g} \sin 45-\mathrm{a})

(P1−P2)=ρd(g−a2)\left(P_{1}-P_{2}\right)=\rho d(g-a \sqrt{2}) β=(P1−P2)ρgd=(1−a2g)\beta=\frac{\left(P_{1}-P_{2}\right)}{\rho g d}=\left(1-\frac{a \sqrt{2}}{g}\right)

When a=g/2,β=0\mathrm{a}=\mathrm{g} / \sqrt{2}, \quad \beta=0

When a=g/2,β=(2−12)\mathrm{a}=\mathrm{g} / 2, \quad \beta=\left(\frac{\sqrt{2}-1}{\sqrt{2}}\right)

Answer key and solution verified before publishing.

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Exam
JEE Advanced 2021
Paper
Paper 1
Subject
Physics
Chapter
Fluid Mechanics
Topic
Variation of Static Pressure Inside a Liquid