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Q1. If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of container is

•  0°
• Obtuse angle
•  Acute angle 
•   90°  

Solution

If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of container will be zero degree

Q2. A fluid is said to be ideal if

• Inviscous and compressible
• inviscous and incompressible
• incompressible
• viscous

Solution

An inviscous and incompressible fluid is said to be an ideal fluid.

Q3. Of the two lubricants A and B for a machine, A has co-efficient of viscocity slightly greater than that of B.  Which would you prefer in summer and winter?

• A in summer and B in winter
• B in summer and A in winter
• A in summer as well as winter
• B in summer as well as winter

Solution

In summers, co-efficient of viscocity of liquid decreases with rise in temperature and in winters, co-efficient of viscocity of liquid increases with fall in temperature.  Hence sample A having greater co-efficient of viscocity is preferred in summers and sample B in winters.

Q4. The rise of a liquid in a capillary tube does not depend upon

•  Radius of the capillary tube 
• Angle of contact 
• Atmospheric pressure
• Density of the liquid

Solution

Atmospheric pressure does not cause rise of a liquid in a capillary tube.

Q5. In which of the following types of flows is the Bernoulli's theorem strictly applicable:

• Streamlined and rotational
• Streamlined and irrotational
• Turbulent and rotational
• Turbulent and irrotational

Solution

In streamline flow, the velocity of flow at any point in the liquid does not vary with time.

Q6. Blood is flowing at the rate of 200 cm³/s in a capillary of cross-section area 0.5 m².  The velocity of flow is mm/s is

• 0.1
• 0.2
• 0.3
• 0.4

Solution

From the equation of continuity (av = constant), we have 0.5 V = 200 X 10^-6 V = 4 X 10^-4 m/s V = 0.4 mm/s.

Q7. Bernoulli's theorem includes as a special case of:

• Pascal's law
• Torricelli's law
• Archimedes' principle
• Hooke's law

Solution

Torricelli's theorem:   Let O be the orifice. The velocity of the liquid at free surface A is zero. According to Bernoulli's theorem, we have P₁+h₁ρ₁g+½ρ₁v₁² = P₂+h₂ρ₂g+½ρ₂v₂² Applying Bernoulli's theorem at A and O, we get [P + hρg + 0]_{at A} = [P + 0 + ½ ρv²]_{at O} P + hρg = P + ½ ρv² hρg = ½ρv² hg = ½v²

Q8. In the houses far away from the municipal water tanks often people find it difficult to get water on the top floor. This happens because

• the viscosity of the water is high
• the pipes are not of uniform diameter
• of loss of pressure during the flow of water
• water wets the pipe

Solution

During the flow of water, a part of pressure energy is dissipated in doing work against friction.

Q9. Water is flowing through a pipe under constant pressure. At some place the pipe becomes narrow. The pressure of water at this place:

• increases
• decreases
• remains the same
• depends on several factors

Solution

According to Bernoulli's theorem P/ρ + ½v² = Constant. At narrow end, velocity increases and hence pressure decreases.

Q10. A garden sprinkler has 150 small holes, each of 2 mm² area. If water is supplied at the rate of 0.3 litres/s, then find the average velocity of the spray.

• 0.1 cm/s
• 22.5 cm/s
• 100 cm/s
• 300 cm/s

Solution

No of holes in the sprinkler is n = 150 Area of each hole is a = 2 mm² Total area of 150 holes is A = 150 × 0.02 = 3 cm² Rate of flow of liquid is V = 0.3 litre/s = 300 cc/s By equation of continuity, we have V = av or v = V/a = 100 cm/s

Q11. Hydraulic brakes use

• Stoke's Law
• Gas Law
• Pascal's Law
• Archimide's Principle

Solution

The working of hydraulic machines is based on Pascal's Law.

Q12. Water flows through a horizontal pipe whose internal diameter is 2.0 cm, at a speed of 1.0 ms^-1. What should the diameter of the nozzle be, if the water is to emerge at a speed of 4.0 ms^-1?

• 1.5 cm
• 1.0 cm
• 4.0 cm
• 2.0 cm

Solution

d₁ = 2 cm = 0.02 m, v₁ = 1 ms^-1 v₂ = 4 ms^-1, d₂ = ? Using the equation of continuity, we have

Q13. A flat plate is separated from a large plate by a layer of glycerine of thickness 3 X 10^-3m.  If the co-efficient of viscocity of glycerine is 2 Nsm², what is the force required to keep the plate moving with a velocity of 6 X 10^-2 m/s. Area of the plate is 4.8 X 10^-3m².

• 192 N
• 19.2 N
• 1.92 N
• 0.192 N

Solution

Q14. The viscosity of gases ________ with increase in temperature

• Increase
• Decrease
• Remain same
• Depends on the type of liquid

Solution

Viscosity of gases is due to diffusion of molecules from one moving layer to another. But the rate of diffusion of gases is directly proportional to the square root of its absolute temperature, and so the viscosity of a gas increases with temperature.

Q15. Air is streaming past a horizontal airplane wing such that its speed is 120 m/s over the upper surface and 90 m/s at the lower surface. If the density of the air is 1.3 kg/m³ and the wing is 10 m long and has an average width of 2 m, then the difference of pressure on the two sides of the wing is

• 4.095 Pa
• 409.5 Pa
• 4095.0 Pa
• 40.95 Pa

Solution

 

Q16. Which of the energy is not related to streamline flow of liquid?

• Potential Energy
• Kinetic Energy
• Pressure Energy
• Surface Energy

Solution

During stream line flow, liquid possesses mainly three kind of energies viz. Potential, Kinetic, and  Pressure energy.

Q17. When the velocity of liquids exceed the critical velocity then

• streamline flow becomes turbulent
• turbulent flow becomes streamlined
• turbulent flow becomes smooth
• streamline flow becomes more smooth

Solution

When the velocity of liquids exceed the critical velocity, then streamline flow becomes turbulent.

Q18. Oil spreads on cold water but may remain as a drop on hot water because:

• surface tension of oil is more than that of cold water
• surface tension of oil is less than that of cold water
• surface tension of oil is more than that of hot water
• Both (b) and (c)

Solution

Surface tension of oil is less than cold water, and hence, oil spreads over cold water. However, surface tension of oil is greater than that of hot water, and hence, its shape remains as a drop.

Q19. Viscosity is the property of fluids by virtue of which they tend to:

• create a relative motion between their layers
• maintain the relative motion between their layers
• destroy any relative motion between their layers
• none of the above

Solution

Viscosity is the property of fluids by virtue of which they tend to destroy any relative motion between their layers.

Q20. To which type of fluid is the Bernoulli's theorem applicable:

• Compressible and anisotropic
• Incompressible and anisotropic
• Incompressible and viscous
• Incompressible, isotropic and non viscous

Solution

To which type of fluid is the Bernoulli's theorem applicable incompressible, isotropic and non viscous.

Q21. A straight or curved path, such that tangent to it at any point gives the direction of flow of liquid at that point is known as

• Turbulent flow
• Streamline flow
• Random flow
• Terminal flow

Solution

A straight or curved path, such that tangent to it at any point gives the direction of flow of liquid at that point is known as streamline flow.

Q22. Streamlines are a map depicting fluid flow. Two streamlines do not intersect because

• Bernoulli's equation will be violated
• a fluid particle cannot have two possible velocities at a point
• it is difficult to draw them in that manner
• the velocity varies as the fluid flows

Solution

Streamlines are a map depicting fluid flow. Two streamlines do not intersect because a fluid particle cannot have two possible velocities at a point.

Q23. A person standing near the track of a fast moving train has a tendency to fall towards it because of:

• Vibration due to motion of train.
• Gravitational force of attraction between person and train.
• the high speed of train
• some other effect.

Solution

Air between person and the train moves with high velocity due to dragging effect and the air behind person is approximately still. Therefore, due to Bernoulli's principle, the pressure between the person and the train decreases and the air behind the person pushes him towards train due to which he falls towards train.

Q24. By which phenomenon does the water rise from roots to leaves of plants?

• Surface Tension
• Viscosity
• Capillary action
• Bernoulli's Theorem

Solution

Water rises from roots to leaves of plants by the phenomenon capillary action.

Q25. When impurity is added to a liquid, its surface tension

• increases
• decreases
• remains same
• first decreases and then increases

Solution

Surface Tension of a liquid decreases when impurity is added to it.

Q26. Paint gun depends upon:

• Boyle's law
• Newton law of motion
• Bernoulli's principle
• Archimedes' principle

Solution

Paint gun depends upon bernoulli's principle.

Q27. A venturimeter is used to

• find viscosity of a fluid
• measure speed of a freely falling body in the fluid
• measure flow speed of incompressible fluid
• measure atmospheric pressure

Solution

Venturimeter measures flow speed of incompressible fluid.

Q28. Rain drops are spherical in shape because of

• Acceleration due to gravity
• Downward motion 
• Capillary
•   Surface tension  

Solution

Surface tension is the physical phenomenon due to which the raindrops arrange themselves in a spherical manner.

Q29. A non-viscous liquid flows through a hose. Liquid enters with velocity 6.4 m/s and leaves with velocity 2.5 m/s. What is the ratio of radii of the hose where the liquid enters and where it leaves?

• 8 : 5
• 5 : 8
• 5 : 1
• 8 : 1

Solution

According to equation of continuity, we have

Q30. Venturimeter is a device used to measure the

• Rate of flow of an incompressible liquid
• Rate of expansion of an ideal gas
• Rate of expansion of a real gas
• Rate of flow of a compressible liquid

Solution

Venturimeter is a device used to measure the rate of flow of an incompressible liquid.

Q31. As the velocity of a body increases, the viscous force on it

• Decreases
• Increases
• Remains unaltered
• Might increase or decrease according to medium

Solution

Viscous force on a body is directly proportional to its velocity. So as velocity increases, the viscous force on the body also increases.

Q32. According to Pascal's Law

• The pressure in a fluid in equilibrium is same everywhere.
• The pressure in a fluid in equilibrium is same at top
• The pressure in a fluid in equilibrium is same near the walls of container.
• The pressure in a fluid in equilibrium is same at the base

Solution

According to Pascal's Law the pressure in a fluid in equilibrium is same everywhere (if gravity is neglected).

Q33. In case of streamlined flow of liquid, the loss of energy is

• minimum
• maximum
• zero
• infinite

Solution

In case of streamlined flow of liquid, the loss of energy is minimum because different layers glide over one another without intermixing. Therefore, there is no collision between the molecules of different layers, and hence minimum energy loss.

Q34. Which of the following cannot be explained using Bernoulli's principle.

• Working of carburetor
• Atomiser
• Descending with parachute
• swing in a fast moving cricket ball

Solution

Descending with parachute can be explained using Stoke's Law.

Q35. The property by virtue of which the free surface of a liquid at rest behaves like an elastic stretched membrane tending to contract so as to occupy minimum surface area is known as

• Surface energy
• Viscosity
• Surface tension
• Bernoulli's principle

Solution

The property by virtue of which the free surface of a liquid at rest behaves like an elastic stretched membrane tending to contract so as to occupy minimum surface area is known as surface tension.

Q36. The liquid that does not wet the solid surface has an ______ angle of contact.

• Acute
• Obtuse
• 90^o
• 60^o

Solution

When liquid molecules are attracted strongly to themselves and weakly to those of solids, it costs lots of energy to create liquid-solid surface and liquid then does not wet the solid.

Q37. The terminal velocity of a steel ball of 4 mm in diameter falling through a glycerin of viscosity 3.3 poise, given relative density of steel is 8, relative density of glycerin is 1.3 is

• 17.47 cm s^-1
• 1.77 cm s^-1
• 1.47 cm s^-1
• 13.23 cm s^-1

Solution

Terminal velocity is   Substituting the values, we get   = 17.47 cm s^-1

Q38. Bernoulli's theorem is important in the field of:

• Photoelectric effect
• Electrical cells
• Magnetism
• Flow of liquids

Solution

Bernoulli's theorem is important in the field of flow of liquids.

Q39. Water is flowing through a tube of non-uniform cross-section.  If the ratio of radius of the tube at the entrance and exit is 3 : 2, then the ratio of velocity of liquid entering and leaving the tube is:

• 8 : 27
• 4 : 9
• 1 : 1
• 9 : 4

Solution

From the equation of continuity, we have A₁V₁ = A₂V₂ Let A₁ = area of cross-section of entrance =  and A₂ = area of cross-section =  V₁ = velocity at entrance V2 = Velocity at exit Therefore, we get

Q40. A value of Reynold's number _________ indicates turbulence.

• R < 2000
• R > 2000
• R < 1000
• R < 100