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JEE Main 2022 (26 Jun, Shift 1) · Bernoulli's Equation

Bernoulli's Equation question from JEE Main 2022 (26 Jun, Shift 1)

Q21JEE Main 2022 · 26 JUN · SHIFT 1Medium

Bernoulli's Equation

An ideal fluid of density 800 kgm−3{}^{-3}, flows smoothly through a bent pipe (as shown in figure) that tapers in cross-sectional area from a to a2\frac{a}{2}. The pressure difference between the wide and narrow sections of pipe is 4100 Pa. At wider section, the velocity of fluid is x6\frac{\sqrt{x}}{6} ms−1{}^{-1} for x = ___________. (Given g = 10 ms−2{}^{-2})

Figure

Numerical answer type. Work it out, then open the answer.

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Answer: 363

  1. Continuity: area a→a2a \to \frac{a}{2}, so v2=2v1v_2 = 2v_1. The wide end is h=1h = 1 m higher.
  2. Bernoulli: P1+12ρv12+ρgh=P2+12ρv22P_1 + \frac{1}{2}\rho v_1^2 + \rho g h = P_2 + \frac{1}{2}\rho v_2^2
  3. (P1−P2)+ρgh=32ρv12⇒4100+800(10)(1)=32(800)v12(P_1 - P_2) + \rho g h = \frac{3}{2}\rho v_1^2 \Rightarrow 4100 + 800(10)(1) = \frac{3}{2}(800)v_1^2
  4. 12100=1200 v12⇒v1=1112=1136=3636 m/s12100 = 1200\,v_1^2 \Rightarrow v_1 = \frac{11}{\sqrt{12}} = \frac{11\sqrt{3}}{6} = \frac{\sqrt{363}}{6}\text{ m/s}
  5. So x=363x = 363.
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