RRB JE Stage II exam is scheduled to be conducted from 28th August to 1st September 2019. The overall merit for the selection will be made on the basis of the marks scored in stage II, so candidates need to prepare thoroughly for the second stage. To help the aspirants, Adda247 has come up with a study plan in which we will provide you daily quizzes of all technical subjects. The below quiz will be helpful for the candidates who opted Mechanical as the exam group in RRB JE stage II.
Q1. Which of the following forces act on a fluid at rest?
1. Gravity force
2. Hydrostatic force
Select the correct answer using the codes given bellow
(a) 1, 2, 3 and 4
(c) 2 and 4
(b) 1,2 and 3
(d) 1,3 and 4
Sol. For a fluid at rest, there can be no shear force (i.e. viscous force), The only forces acting on the free body are the normal pressure forces, exerted by the surrounding fluid on the plane surface and the weight of the element.
Q2. Surface tension is due to
(a) viscous forces
(d) the difference between adhesive and cohesive forces
Sol. Surface tension is due to cohesion between liquid particles at the surface, where as capillarity is due to both cohesion and adhesion The property of cohesion enables a liquid to resist tensile stress, while adhesion enables it to stick to another body
Q3. Newton’s law of viscosity depends upon the
(a) stress and strain in a fluid
(b) shear stress, pressure and velocity
(c) shear stress and rate of strain
(d) viscosity and shear stress
Sol. Newton’s law of viscosity
where τ= shear stress,
du/dy=rate of strain
Q4. The normal stress is the same in all directions at a point in a fluid only when
(a) the fluid is frictional
(b) the fluid is frictionless and incompressible
(c) the fluid has zero viscosity and is at rest
(d)one fluid layer has no motion relative to an adjacent layer
Sol. The pressure at any point in a fluid at rest has the same magnitude in all directions. In other words, when a certain pressure is applied at any point in a fluid at rest, the pressure is equally transmitted in all the direction and to every other point in the fluid. It is known as Pascal’s law
Q5. A capillary tube is inserted in mercury kept in an open container.
Assertion (A): The mercury level inside the tube shall rise above the level of mercuryoutside.
Reason (R): The cohesive force between the molecules of mercury is greater than the adhesive
force between mercury and glass
(a) Both A and R are individually true and R is
the correct explanation of A
(b) Both A and R are individually true but R is
not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Sol. The assertion is false but the reason is true because for mercury the cohesive force is greater than adhesive force. So there is a dip (not rise) in the capillary tube
Q6. An oil of specific gravity 0.9 has viscosity of 0.28 stokes at 38°C. What will be its viscosity in Ns/m2?
Sol. Dynamic viscosity,
μ=ρν=(0.9 x 1000) x (0.28 x 10¯⁴)
Q7. Assertion (A): In general, viscosity in liquids increases and in gases it decreases with rise in temperature.
Reason (R): Viscosity is caused by intermolecular forces of cohesion and due to transfer of molecular momentum between fluid layers; of which in liquids the former and in gases the later contribute the major part towards viscosity.
(a) Both A and R are individually true and R is the correct explanation of A
(b) Both A and R are individually true but R is not the correct explanation of A
(c) A is true but R is false
(d) Ais false but R is true
Sol. In liquid, viscosity is due to cohesion with rise in temperature, volume of liquid increases, the
distance between molecules increases, thus decreasing the cohesion. Therefore the viscosity of liquid decreases with rise in temperature. In case of gases, viscosity is due to molecular momentum exchange with rise in temperature of gas, kinetic energy of molecules increases, thus increasing the molecular momentum exchange. Therefore, the viscosity of gases increases with rise in temperature
Q8. Consider the following statements:
2. Surface tension
4. Vapour pressure
Which of the above properties can be attributed to the flow of jet of oil in an unbroken stream?
(b) 2 only
(c) 1 and 3
(d) 2 and
Sol. Viscosity is that property of a fluid by virtue of which it offers resistance to the movement of one layer of fluid over an adjacent layer.
Q9. When the pressure on a given mass of liquid is increased from 3.0 MPa to 3.5 MPa, the density of the liquid increases from 500 kg/m3 to 501 kg/m3. What is the average value of bulk modulus of liquid over the given pressure range?
(a) 700 MPa
(b) 600 MPa
(c) 500 MPa
(d) 250 MPa
Sol. Solution :- Bulk modulus,
=(500 x(3.5-3.0)) /(501-500)
Q10. Consider the following statements related to the fluid properties:
1.Vapour pressure of water at 373 K is 101.5 x 10^3 N/m^2
2.Capillary height in cm for water in contact with glass tube and air is ( tube diameter) /0.268
3.Blood is a Newtonian fluid.
Which of these statements is/are correct?
(a) 1 only
(b) 1 and 3
(c) 1 and 2
(d) 2 only
Sol. Only first statement is correct.
(i) Vapour pressure of water at 373 K is 101.5 x 10^3 x N/m^2
(ii) Capillary height in cm for water in contact with glass tube is 0.3/d
(iii)Blood is a pseudoplastic fluid.
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