# Class 11th Physics – 10 Mechanical properties of fluids MCQs

#### If a small hole is made at a height of 1/√2 m from the bottom of a cylindrical water tank and at a depth of h = √2 m from the upper level of water in the tank, then the water emerging from the hole would strike the ground at a distance of ____.

#### The density of the atmosphere at sea level is 2.50 kg/m^{3}. If it does not change with altitude, then the atmosphere would extend for ____.

Here, density (d) = 2.50 kg/m3 acceleration due to gravity (g) = 9.8 m/s2 atmospheric pressure (P) 1.01 × 105 Pa

Then, P = hdg

1.01 × 105 = h × 2.50 × 9.8

1.01×105/2. 50×9. 8= h

h = 3.959 km

#### A square plate of area 3 sq. metres is separated from a large plate by a layer of oil 3 mm thick. If coefficient of viscosity of this oil is 0.01 Pa s, then the force required to keep the plate moving with a velocity of 6 cm/s is ____.

A square plate of area 3 sq. metres is separated from a large plate by a layer of oil 3 mm thick. If coefficient of viscosity of this oil is 0.01 Pa s, then the force required to keep the plate moving with a velocity of 6 cm/s is ____.

#### The liquid used in a digital sphygmomanometer is ____.

There is no liquid used in a digital sphygmomanometer.

#### Blood pressure is due to the force exerted by circulating blood on the walls of ____.

Blood pressure is due to the force exerted by circulating blood on the walls of blood vessels, namely arteries and veins.

#### Consider that a barometer tube is inclined at an angle of 60° with the horizontal direction. If the atmospheric pressure is 65 cm of Hg, the length of mercury column in the barometer tube will be ____.

Here, h = 65 cm sin600=√3/2 1=h/sin600 =(65)/(√3/2) =65×2/√3= 75 . 05 cm

#### The press plunger of a hydraulic pressure is 5 m^{2} in cross-section and is required to overcome a resistive load of 500 kg f . If the area of cross-section of the press plunger is 0.01 m^{2}, then the force required on the pump plunger will be ____.

Let F be the force required on the pump plunger. By Pascal's law, Pressure on pump plunger = Pressure on press plunger F/0 .01 = 500/5 Therefore, F = 0.01 × 100 = 1 kg f

#### Surface tension may be defined as ____.

Surface tension = Work done per unit area in increasing the surface area of a liquid under isothermal conditions.

#### Which of the following is true regarding condition for a Venturimeter to measure the rate of flow of a liquid?

For measuring the rate of flow of a liquid by a Venturimeter, the liquid should be incompressible.

#### If the flow of water in a tube of diameter 3 cm is linear, then the average velocity of water is____. (Note: Assume viscosity of water is 0.001 Pa-s)

Here, D = 3 cm = 0.03 m, η = 0.001 Pa-s, ρ = 10^{3} kg/m^{3}

Thus, for a stream line flow, N_{R} = 2000

∴v = NRη/ρD = 2000×0 . 001/10^{3}×0. 03 = 0.07 ms^{-1}

#### An incompressible fluid flows steadily through a cylindrical pipe which has radius 2R at point A and radius R at point B farther along the flow direction. If the velocity at point A is v, then its velocity at point B will be____.

From equation of continuity, Π (2R)^{2} v = Πr^{2} v_{1}

Therefore, v_{1} = 4 v

#### What is the principle on which Venturimeter is based?

A Venturimeter is developed based on Bernoulli’s principle.

#### Three exactly similar rain drops falling with terminal velocity 3 ms^{-1 }coalesce to form a bigger drop. The new terminal velocity of the bigger drop will be____.

Volume of bigger drop = Volume of three small drops

4/3 π R^{3} = 3×4/3 π r^{3}

⇒R^{3} = 3r^{3} or R/r = 3^{1/3}

Terminal velocity of the smaller drop v_{1}= (2/9)(r^{2}/η) (ρ- σ)g

Terminal velocity of the bigger drop v_{2}= 2/9 R^{2 }/η(ρ−σ)g

∴v_{2}/v_{1 }= R^{2}/r^{2 } = 3^{1/3}= 3^{2/3}

∴v_{2}= 3^{2/3}×3 = 3^{5/3 }ms^{-1}

#### The surface tension of a liquid at critical temperature is ____

The surface tension of a liquid at critical temperature is zero.

#### If liquid rises in a tube due to capillary action, the angle of contact would be ____.

If liquid rises in a capillary tube, then h is positive. Therefore, cos θ is +ve. If cos θ is +ve, θ < 90° or θ is acute.

#### If a non-wetting liquid is displaced in a capillary tube, the shape of the liquid when seen from below would be ____ .

Being a non-wetting liquid, it will not wet the sides of capillary tube and hence, will have a meniscus convex upwards. The angle of contact will be greater than 90°. So, when the upwards convex meniscus is seen from below, it will look as concave downwards.

#### Surface tension of a liquid is due to ____.

Surface tension of a liquid is due to force of attraction between like molecules of a liquid i.e., cohesive force between molecules.

#### If temperature increases, angle of contact ____.

When the temperature increases, the surface tension of the liquid decreases. As surface tension is indirectly proportional to angle of contact, angle of contact increases.

#### If the level of water in a tank is 5 m high and a hole of area 1 cm^{2} is made in the bottom of the tank, then the rate of leakage of water from the hole will be ____. (assume g = 10 ms^{-2})

Here, Velocity of efflux v = √2gh, Volume of liquid flowing out per second =v×A = √ (2gh)×A = √(2×10×5)× 10^{- 4}=10^{- 3}m^{3}/s

#### In a hydraulic machine, the two pistons have area of cross-section in the ratio 1:10. The force needed on the narrow piston to overcome a force of 100 N on the wider piston is ____ .

A_{1} = 1 A_{2} = 10 F_{1 }=? F_{2} = 100 N

By the principle of hydraulic machine,

F_{1}/A_{1} = F_{2}A_{2}

F_{1}/1 = 100/10

Therefore, F_{1} = 10 N

#### The intermolecular distance is the least in ___ and the highest in ___.

The intermolecular distance is the least in solids and the highest in gases.

#### Fluids are

The material that has the property to flow is referred to as a fluid. Hence, both liquids and gases combined together are called fluids.

#### In a streamline flow, the velocity of flow at a point in the liquid ____

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

#### In Bernoulli's theorem, ____ is conserved.

According to Bernoulli's theorem, only law of conservation of energy is maintained.

#### Bernoulli's equation is important in the field of____

Bernoulli's theorem is an indispensable tool for the analysis of flow of liquids.

#### The SI unit of pressure is ____.

Pressure is force per unit area. Hence, the SI unit of pressure is the ratio of SI unit of force to SI unit of area, which is N/m^{2}.

#### The concentration of streamlines around a ball in motion through air represents the ____.

The concentration of streamlines around a ball in motion through air represents the magnitude of velocity of air.

#### A square flat plate of side 25 cm moves over another similar plate with a thin layer of 0.4 cm of a liquid between them. If a force of 1 kg.wt moves one of the plates uniformly with a velocity of 1 ms^{-1}, then the coefficient of viscosity will be ____. (Assume g = 9.8 × ms^{-2})

Here, A = 25 × 25 = 625 × 10^{-4} m^{2}, F =1 kg.wt = 1 × 9.8 N; dv = 1 ms^{-1}; dx = 0.4 cm = 0.4 × 10^{-2} m

So, η = F/A(dvdx) = F dx/A dv = 9 . 8×0. 4×10^{- 2}/625×10^{- 4}×1 = 0. 63 Pa s

#### The dynamic lift due to the additional spin motion of a ball along with its translational motion in air is also called the Magnus effect.

The dynamic lift due to the additional spin motion of a ball along with its translational motion in air is also called the Magnus effect.

#### The blood vessels that carry blood from the heart to other parts of the body are _____ and those that return blood to the heart are ____.

The blood vessels that carry blood from the heart to other parts of the body are arteries and those that return blood to the heart are veins.

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