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# Fluid Mechanics (421-442)

Updated: Apr 24, 2020

a) Both A and R are true and R is the correct explanation of A

b) Both A and R are true but R is not a correct explanation of A

c) A is true but R is false

d) A is false but R is true

421. Assertion A : At the critical state of flow, the specific force is a minimum for the given discharge.

Reason R :For a minimum value of the specific force, the first derivative of force

with respect to depth should be unity

C

422. Assertion A : The Specific speed of a Pelton wheel is generally much less than

that of a reaction turbine.

Reason R : Pelton wheels generally use more than one nozzle and the specific

speed is defined for power developed per nozzle. b

423. Assertion A : Pressure intensity in a liquid flow is a form of energy.

Reason R : The pressure gradient is a measure of the rate of energy dissipation

424. Assertion A : The following potential function in two-dimensional flow field

represents rotational flow Φ = 2x² - 3y² Reason R : For the given function d

425. Assertion A : In Rayleigh's method of dimensional analysis, the dependent variable is written as the function of exponential terms of independent variables.

Reason R : In Rayliegh's method, when the number of independent variable

exceeds three, the exponents of non repeating variables are expressed as the

exponents of repeating variables. b

426. Assertion A : If laminar flow of oil between two points of a given pipeline is

doubled, then the power consumption is increased to four times the original power.

Reason R : In laminar flow through circular pipes, head loss varies directly as

the discharge a

427 Assertion A : In the equation for laminar flow through the pipe, the term v (mean velocity of flow) is given by Reason R : The term T (friction factor) in the above equation equals 64/Re , where

a

428. Assertion A : Water flows through a pipe connecting two reservoirs. The line

joining the water surface levels in the reservoirs is the hydraulic gradient

Reason R : There will be no negative gauge pressure anywhere in the pipeline,

as long as the pipeline lies below the hydraulic gradient. b

429. Assertion A : Irrotational flow exists when the net rotation of the fluid about

its mass centre is zero.

Reason R: There is always a possibility of rotation in ideal fluid and therefore, ideal fluids cannot have irrotational flow.

c

430. Assertion A : The inlet velocity triangle for a Pelton turbine is a straight line

Reason R : For a Pelton turbine, the vane angle at inlet is 180° a

431. Assertion A : A minor change in specific energy at or close to critical state

will cause a major change in depth.

Reason R: A critical state of flow is characterized by its Froude number being

equal to unity. b

432. Assertion A : The movement of two blocks of wood wetted with hot glue

requires greater and greater effort as the glue is drying up.

Reason R : Viscosity of liquids varies inversely with temperature

a

433. Assertion A : There is no flow in the direction perpendicular to a stream line at

any point on it.

Reason R : Stream line consists of a number of infinitesimally small segments

such that all of them lie along the directions of velocity vectors of fluid

particles at those segments

a

434. Assertion A : Continuity equation must hold good in a pipe network system.

Reason R : In a pipe network analysis, the flow into any junction must be equal

to the flow out of the junction. a

435. Assertion A : Water hammer occurs when the quick-acting valve at the end of a long pipeline is suddenly closed.

Reason R : Surge tanks are provided in penstocks to relieve the penstock of high

water hammer pressure when the flow into a turbine is stopped due to low power

demand a

436. Assertion A : In the standing-wave flume, flow occurs in a super-critical state

so that discharge can be related to a depth upstream of flow

Reason R : A standing wave flume is a venturi flume operating under one

condition in which a hydraulic jump is formed. d

437.Assertion A : The discharge (Q) through a triangular weir is given by where Cd is the coefficient of discharge, h is the head of flow, 6 is the apex angle

of the weir and g is the acceleration due to gravity.

Reason R : The cross-sectional area of flow in a triangular weir is h2 tan (9/2) and

average velocity is a

438. Assertion A : When both gravitational and viscous forces are predominant in a flow scale ratio can be chosen at will.

Reason R : With both gravitational and viscous forces being predominant, scale

ratio depends upon kinematic viscosity of the fluids. d

439. Assertion A : Any discharge will flow as critical in a wide rectangular channel

whose bed slope is 1 in C²/g

Reason R :The critical depth of flow through a wide rectangular channel is (q²/g)¹/³ a

440. Assertion A : Loss of head at a sudden expansion in a pipe is greater

than that at a sudden contraction.

Reason R : Flow in a sudden expansion tends to be irrotational. c

441. Assertion A : The kinematic viscosity of both air and water decreases as the

temperature increases.

Reason R : The kinematic viscosity of liquids and gases at a given pressure is a

function of temperature d

442. Assertion A : Energy is lost in sudden contraction in a pipeline.

Reason R : If the flow is now reversed, energy can be gained at the transition which acts as an expansion c