Fluids And Pressure Test

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Fluids And Pressure Test - 6

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Question 1
1 / -0

When a body is fully or partially immersed in a liquid, it appears to lose weight. This loss of weight is equal to the weight of

A
water displaced by the body

B
liquid displaced by the body

C
equal volume of water

D
equal volume of liquid

Solution

The loss in weight of a body when it is partially or fully immersed in water is equal to the volume of the liquid displaced by the body. This is called Archimedes' principle.
Question 2
1 / -0

When a body is weighed in a liquid, the loss in its weight depends upon

A
volume of the body

B
mass of the body

C
shape of the body

D
centre of gravity of the body

Solution

From the Archimedes principle, the loss in weight of a body when it is partially or fully immersed in a liquid depends on the volume of liquid displaced by it. Now, the volume of liquid displaced is same as the volume of body which is fully or partially immersed in the liquid.
Question 3
1 / -0

Which of the following would a hydrogen balloon find easier to lift?

A
1 kg of water

B
1 kg of steel

C
1 kg of light packed feather

D
All of the above

Solution

1 kg of light packed feather would a hydrogen balloon find easier to lift.
Question 4
1 / -0

A vessel with water is placed on a weighing scale. The weighing scale reads 600 g. Now, a ball of 40 g and density 0.80 g/cc is sunk into the water with a pin as shown in the figure, keeping it sunk. The final reading of the weighing scale will be

A
600 g

B
550 g

C
650 g

D
640 g

Solution

Volume of the ball = 40/0.8 = 50 cc
Upthrust = 50 * 1 g
So, the net weight will be = 600 g + 50 g = 650 g.
Question 5
1 / -0

A cork of density 250 kgm^-3 floats in a liquid with one-third of its volume below the surface of the liquid. Find the density of the liquid.

A
700 kgm^-3

B
720 kgm^-3

C
750 kgm^-3

D
800 kgm^-3

Solution

Buoyancy = Weight of cork
Symbols with 1 represent properties of fluid, while those with 2 represent properties of cork.
Buoyancy = Volume of immersed body x Density of fluid x g
= V x ρ_₁ x g ............ eq 1
V = Volume of cork immersed
Weight of cork = m_₂ x g = ρ_₂ x V_₂ x g ............ eq 2
V x ρ_₁ x g = ρ_₂ x V_₂ x g
V x ρ_₁ = ρ_₂ x V_₂
V = ⅓ V_₂
⅓V_₂ x ρ_₁ = ρ_₂ x V_₂
⅓ x ρ_₁= ρ_₂
ρ_₁ = 3 x ρ_₂
= 3 x 250 kg/m^Â³
= 750 kg/m^Â³
Question 6
1 / -0

When a piece of ice melts in water, the level of water

A
rises

B
falls

C
remains the same

D
first rises, then falls

Solution

When a piece of ice melts in water the level of water remains the same. This is because the water displaced by the ice is same as the mass of the ice.
Question 7
1 / -0

Two solids - A and B - float in a liquid. It is observed that A floats with half its volume immersed and B floats with (2/3) of its volume immersed. Find the ratio of densities of A and B.

A
4 : 3

B
2 : 3

C
3 : 4

D
1 : 3

Solution

Let the density of A = ρ_A, Volume = V_A
Let the density of B = ρ_B, Volume = V_B
Let the density of liquid be ρ.
V_Aρg = V_Aρ_Ag for A - (1)
V_Bρg = V_Bρ_Bg for B - (2)
From (1), ρ_A = and from (2), ρ_B= ρ
= ρ_A : ρ_B = ^:ρ_A:_^ρB= 3 : 4
Question 8
1 / -0

A man is sitting in a boat, which is floating in a pond. If the man drinks some water from the pond, the level of water in the pond will

A
rise a little

B
sink a little

C
remain stationary

D
none of the above

Solution

The level of water in the pond will remain the same.
Question 9
1 / -0

Water flows through a frictionless duct with a cross-section varying as shown in the figure.

The pressure p at points along the axis is represented by

A

B

C

D

Solution

From the Bernoulli`s equation, the energy per unit volume before and after a liquid flows through a constriction, is the same.
When the fluid flows through a constriction, its speed increases and its pressure decreases given by,

If V₂ > V₁
Then,
Hence,
Question 10
1 / -0

A large open tank has two holes in the wall. One is a square hole of side L at a depth y form the top and the other is a circular hole of radius R at a depth 4y from the top. When the tank is completely filled with water, the quantity of water flowing out per second from both holes is the same. Then R, is equal to

A

B
2

C
L

D

Solution

Velocity at depth v = Using, A₁v₁= A₂v₂
Question 11
1 / -0

The principle of operation of a Brahma's press is based on

A
Boyle's law

B
Pascal's law

C
Dalton's law

D
Newton's law

Solution

It is a hydraulic press and hence is based on Pascal`s law.
Question 12
1 / -0

When cooking oil is heated in a frying pan, the oil moves around in the pan more easily, when it is hot. The main reason for this is that with rise in temperature, there is a decrease in

A
surface tension

B
viscosity

C
angle of contact

D
density

Solution

With the rise in temperature, there is a decrease in the viscosity of a fluid. Hence, the oil moves freely when it is hot because it is less viscous.
Question 13
1 / -0

A raindrop reaching the ground with terminal velocity has momentum p. Another drop of twice the radius, also reaching the ground with terminal velocity will have the momentum

A
4p

B
8p

C
16p

D
32p

Solution

Let terminal velocity be V.
Let radius of smaller rain drop = r

Then, other rain drop
{Momentum}

x = 8P
Question 14
1 / -0

A force of 10 kg weight is applied on the head of a nail. The area of cross-section of the tip of the nail is 0.0001 cm². What is the pressure?

A
10¹⁰ Nm^-2

B
10⁶ Nm^-2

C
10^-6 Nm^-2

D
10^-10 Nm^-2

Solution

=
Question 15
1 / -0

A massless conical flask filled with liquid is kept on a table in vacuum. The force exerted by the liquid on the base of the flask is W₁. The force exerted by the flask on the table is W₂. Which of the following relations holds true?

A
W₁ = W₂

B
W₁ > W₂

C
W₁ < W₂

D
The force exerted by the liquid on the walls of the flask is (W₁ + W₂).

Solution

The correct relation is W₁ > W₂.
Question 16
1 / -0

A liquid of density p comes out with a velocity v from a horizontal tube of area of cross–section A. The reaction force exerted by the liquid on the tube is F. Which of the following relations is incorrect?

A
Fv

B
Fv²

C
FA

D
F p

Solution

Volume of liquid discharge per second = V * 1 * AMass of this liquid is V.A.Momentum of this liquid is v² . A.
Question 17
1 / -0

As a bubble comes from the bottom of a lake to the top, its radius

A
increases

B
decreases

C
does not change

D
becomes zero

Solution

As a bubble comes from the bottom of a lake to the top, its radius increases because the pressure exerted by the water in the lake decreases as the bubble moves up.
Question 18
1 / -0

The ratio of the diameters of an air bubble at the bottom and at the surface is 1:2.If 1 atmosphere is equal to pressure of 10 m long water column,then what is the depth of the lake?

A
50 m

B
60 m

C
70 m

D
80 m

Solution

When the diameter doubles,radius doubles.Volume increases by factor of 8.(h+10)V = 10 * 8 Vh = 80 - 10 = 70 m
Question 19
1 / -0

The force of cohesion is the greatest in

A
solids

B
liquids

C
gases

D
do not know

Solution

Solids have maximum force of cohesion as compared to the liquids and gases.
Question 20
1 / -0

Two glass plates are put together with a few drops of water between them. Then it becomes difficult to separate the two by pulling in opposite direction on account of

A
Friction

B
Surface Tension

C
Atmospheric Pressure

D
None of the above

Solution

Surface tension makes it hard to separate the two glass plates in which some drops of water are put.