Fluid Mechanics | Surface Tension And Viscosity | JEE Main previous year questions with Solutions

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Topic Question Set

Q 1 :
Correct Bernoulli's equation is (symbols have their usual meaning) [2024]

$P + ρ g h + \frac{1}{2} ρ v^{2} = c o n s \tan t$
$P + ρ g h + ρ v^{2} = c o n s \tan t$
$P + m g h + \frac{1}{2} m v^{2} = c o n s \tan t$
$P + \frac{1}{2} ρ g h + \frac{1}{2} ρ v^{2} = c o n s \tan t$

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(A) $P + ρ g h + \frac{1}{2} ρ v^{2} = c o n s \tan t$

Energy per unit volume is conserved.

Q 2 :
The reading of pressure metre attached with a closed pipe is $4.5 \times 10^{4} N / m^{2}$ . On opening the valve, water starts flowing and the reading of pressure metre falls to $2.0 \times 10^{4} N / m^{2}$ . The velocity of water is found to be $\sqrt{V} m / s$ . The value of V is ___________ . [2024]

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(50) $Change in pressure = \frac{1}{2} ρ v^{2}$

$4.5 \times 10^{4} - 2 \times 10^{4} = \frac{1}{2} \times 10^{3} \times v^{2}$

$2.5 \times 10^{4} = \frac{1}{2} \times 10^{3} \times v^{2}$

$v^{2} = 50$

$v = \sqrt{50}$

Q 3 :
A plane is in level flight at constant speed and each of its two wings has an area of $40$ $m^{2}$ . If the speed of the air is 180 km/h over the lower wing surface and 252 km/h over the upper wing surface, the mass of the plane is __________ kg.

$(T a k e a i r d e n s i t y t o b e 1 k g$ $m^{- 3}$ $a n d$ $g = 10$ $m s^{- 2})$ [2024]

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(9600) By Bernoulli's equation

$P_{1} + \frac{1}{2} ρ v_{1}^{2} = P_{2} + \frac{1}{2} ρ v_{2}^{2}$

$\frac{1}{2} \times ρ \times [4900 - 2500] = \frac{m g}{A}$

$\frac{1}{2} \times 1 \times 2400 = \frac{m \times 10}{80}$

$m = 9600 kg$

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