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Pressure exerted by liquids and gases - class-IX

Description: pressure exerted by liquids and gases
Number of Questions: 59
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Tags: forces in fluids force and pressure pressure floating bodies force motion, force and pressure forces and matter floatation physics mechanics fluids properties of matter
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The magnitude of buoyant force acting on an object immersed in a liquid depends on
  1. Volume of object immersed in the liquid.
  2. Density of the liquid.

  3. Both A and B

  4. None


Correct Option: C
Explanation:

According to Archimedes Principle, the magnitude of buoyant force experienced is equal to the weight of liquid displaced by it by being placed in it.

Hence $B=V _{immersed}\rho g$
Hence $B$ depends both on $V _{immersed}$ and $\rho$.
Correct answer is option C.

The property of a fluid to exert a buoyant force on an object immersed in it is known as _______.

  1. Adhesion

  2. Buoyancy

  3. Cohesion

  4. none of these


Correct Option: B
Explanation:

The property of fluid to exert a buoyant force on an object immersed in it known as Buoyancy .

so  option (B) is correct

When a body is partially or completely immersed in a fluid at rest, it experiences an upthrust which is equal to the weight of the fluid displaced by it.

  1. True

  2. False


Correct Option: A
Explanation:

The given statement is the statement of archimedes principle , so it is true 

hence option (A) is correct

The upward force exerted by the floating body on the fluid is known as upthrust.

  1. True

  2. False


Correct Option: B
Explanation:
Upthrust is the upward force acting on the floating body and is exerted by the fluid .
so given statement is false

hence option (B) is correct

How much is the hydrostatic pressure exerted by water at the bottom of a beaker? Take the depth of water as 45 cm. (density of water $10^3 kg m^{-3})$.

  1. 2410 Pa

  2. 3410 Pa

  3. 4410 Pa

  4. 5410 Pa


Correct Option: C
Explanation:

$Height=45 cm=0.45 m$,
$gravity=9.8 ms^{-2}$
$Density=1000 kg m^{-3}$
$Pressure=hdg$
$=0.45\times 9.8\times 1000Pa=4410 Pa$.

The pressure in a water pipe on the second floor of a building is 60,000 Pa, and on the third floor it is 30,000 Pa. Find the height of the second floor. (Density of water $=1000 kg m^{-3}, g=10 m s^{-2})$.

  1. 3 m

  2. 4 m

  3. 5 m

  4. 6 m


Correct Option: A
Explanation:

Second floor :
$P _1=60,000 Pa, g=10 ms^{-2}$
$P _1=h _1dg$


$60,000=h _1\times 1000\times 10$

$h _1=\dfrac {60,000}{1000\times 10}=6 m$

[where $h _1=$ height of water tank above second floor]

Third floor :
$P _2=30,000 Pa, g=10 m s^{-2}$,


$\therefore 30,000=h _2\times 1000\times 19$

$\Rightarrow h _2=\dfrac {30000}{1000\times 10}=3 m$

[where $h _2=$ height of water tank above first floor]

$\therefore $ height of the second floor
$=h _1-h _2=6m-3m=3m$

The pressure in water pipe at the ground floor of a building is 120000 Pa, where as the pressure on a third floor is 30000 Pa. What is the height of third floor?
[Take $g=10 m s^{-2}$, density of water $=1000 kg m^{-3}]$.

  1. 9 m

  2. 10 m

  3. 11 m

  4. 12 m


Correct Option: A
Explanation:

Difference in pressure of water at ground floor and third floor
$=(120000-300000)=900000 Pa$
Density of water $=1000 kg m^{-3}$
Let 'h' be the height third floor.
$P=hdg$
$h=\dfrac {p}{dg}=\dfrac {90000}{1000\times 10}=9m$.

The pressure of water on the ground floor is 50000 Pa and at the first floor is 20000 Pa. Find the height of the first floor. Take density of water is $10^3 kg m^{-3}$ and $g=10 ms^{-2}$

  1. 2 m

  2. 3 m

  3. 4 m

  4. 5 m


Correct Option: B
Explanation:

Pressure on the ground floor $=$ Pressure on the first floor + hdg
$\Rightarrow 50000=20000+hdg$
$\Rightarrow 50000=20000+h\times 10^3\times 10$
$\Rightarrow h\times 10^4=50000-20000$
$\Rightarrow h=\frac {30000}{10000}m$
$\Rightarrow height=3 m.$

Calculate the pressure exerted by 0.8 m vertical length of alcohol of density $0.8 g cm^{-3}$. (Acceleration due to gravity $(g)=10 m s^{-2})$.

  1. 3200 Pa

  2. 6400 Pa

  3. 800 Pa

  4. 5000 Pa


Correct Option: B
Explanation:

Vertical length of the alcohol column
$(h)=0.8 m$
Density of alcohol $(d)=0.8 g cm^{-3}$
$=0.8\times 1000=800 kg m^{-3}$
$[\therefore 1 g cm^{-3}=1000 kg m^{-3}]$
$Pressure = hdg$
$=0.8\times 800\times 10$
$=6400 Pa$
Therefore, pressure exerted by the alcohol column is 6400 Pa.

Calculate the pressure exerted by water at the bottom of a lake of depth 6 m. (Density of water $=1000 kg m^{-3}, g=10 ms^{-2})$.

  1. $2\times 10^4 Pa$

  2. $4\times 10^4 Pa$

  3. $6\times 10^4 Pa$

  4. $8\times 10^4 Pa$


Correct Option: C
Explanation:

Height $(h)=6 m$,

$density=1000 kg m^{-3}$,

$g=10 m s^{-2}, Pressure = ?$

$P=hdg$

$=6\times 1000\times 10 Pa$
$=60000 Pa$
$=6\times 10^4 Pa.$

Calculate the vertical height of a mercury column which exerts a pressure of 81600 Pa. (Density of mercury is $13.6 g cm^{-3}$ and $g=10 ms^{-2})$.

  1. 0.2 m

  2. 0.4 m

  3. 0.6 m

  4. 0.8 m


Correct Option: C
Explanation:

$Pressure (P)=81600 Pa$
$Density (d)=13.6 g cm^{-3}$
$=13.6\times 1000 kg m^{-3}$
$(\therefore 1 g cm^{-3}=1000 kg m^{-3})$

Acceleration due to gravity $(g)=10 ms^{-2}$
$P=hdg$
$\Rightarrow h=\dfrac {P}{dg}=\dfrac {81600}{13.6\times 1000\times 10}$
$\Rightarrow h=0.6 m$
Therefore, vertical height of mercury column is 0.6 m.

A liquid of density $12 kg m^{-3}$ exerts a pressure of 600 Pa at a point inside a liquid. What is height of liquid column above that point? $[g=10 ms^{-2}]$

  1. 4 m

  2. 5 m

  3. 6 m

  4. 7 m


Correct Option: B
Explanation:

$Denstiy = 12 kg m^{-3}, Pressure=600 Pa$
$Pressure=hdg$
$\Rightarrow hdg=Pressure\Rightarrow height=\dfrac {P}{dg}$
$=\dfrac {600}{12\times 10}m=5m.$

A metal cube is placed in an empty vessel. When water is filled in the vessel so that  cube is completely immersed in the water, the force on the bottom of the vessel in contact with the cube-

  1. Will increase

  2. Will decrease

  3. Will remain the same

  4. Will become zero


Correct Option: C

Standing liquid exerts pressure on the bottom due to its:

  1. mass

  2. weight

  3. both mass and weight

  4. none of these


Correct Option: C
Explanation:

Every liquid has a density and volume which implies that it has mass & all the bodies having under gravity exerts weight.

A tank filled with water is placed in vacuum. The net pressure at point which is $10 m$ below the surface of water will be $(g = 10 m/s^2)$

  1. $100 \ kPa$

  2. $10 \ kPa$

  3. $1 \ kPa$

  4. Zero


Correct Option: B
A fluid exert pressure 
  1. only downwards

  2. only upwards

  3. in all directions

  4. Fluids do not exert pressure


Correct Option: C
Explanation:

A fluid is a substance that has no fixed shape and yields easily to external pressure; a gas or  a liquid.

Pressure is exerted by fluids because of their weight. Static fluid pressure is exerted by the depth of the fluid, the density of the fluid and the acceleration of gravity. They exert pressure in all directions, which is given by $F=PA$
where $P$ is the pressure, and $A$ is the area on which force acts.

Which of the following can exert pressure
  1. Solids

  2. Liquids

  3. Gases

  4. All of the above


Correct Option: D
Explanation:

A fluid is a substance that has no fixed shape and yields easily to external pressure; a gas or  a liquid.

Pressure is exerted by fluids because of their weight. Static fluid pressure is exerted by the depth of the fluid, the density of the fluid and the acceleration of gravity.
Well knowingly, the solids exert pressure on the surface on which they are placed, given by $P=\dfrac{mg}{A}$
Hence correct answer is option D.

Which of the following is true?

  1. Fluid do not have any weight

  2. Only liquids have weight

  3. Only gases have weight

  4. Fluids have weight


Correct Option: D
Explanation:

A fluid is a substance that has no fixed shape and yields easily to external pressure; a gas or  a liquid.

Pressure is exerted by fluids because of their weight. Static fluid pressure is exerted by the depth of the fluid, the density of the fluid and the acceleration of gravity.

Two stretched membranes of area $2 cm^2$ and $3 cm^2$ are placed in a liquid at the same depth. The ratio of the pressure on them is :

  1. $1 : 1$

  2. $2 : 3$

  3. $3 : 2$

  4. $2^2 : 3^2$


Correct Option: A
Explanation:

pressure depends on depth not on area so the two stretched membrane would  have  equal pressure.

so ratio of their pressures would be 1 : 1.
hence option (A) is correct

Fill in the blank

Fluids at a given depth exert ______ pressure in all directions 

  1. same

  2. independent

  3. different

  4. zero


Correct Option: A
Explanation:

Fluids at a given depth exert same pressure in all directions.
Pressure of a liquid is directly proportional to the depth, and for a given depth the liquid exerts the same pressure in all directions according to Pascal's law.

The most characteristic property of a liquid is :

  1. elasticity

  2. fluidity

  3. formless

  4. volume conservation


Correct Option: D
Explanation:

a liquid is  substance that flows freely but is of constant volume, having a consistency like that of water or oil.
The most characteristic feature is volume conserrvation.

A block of wood floats separately in river water and then in ocean water. Then the weight of the displaced river water is

  1. equal to the weight of the displaced ocean water.

  2. less than the weight of the displaced ocean water.

  3. more than the weight of the displaced ocean water.

  4. not dependent on the density of the wooden block.


Correct Option: A

The pressure exerted by liquid on container 

  1. increases with depth

  2. decreases with depth

  3. remains unchanged with depth

  4. none of the above


Correct Option: A
Explanation:

$\because p = h\times d\times d$
where, p = pressure
             h = depth
             d = density
so when depth is increases pressure is also increases.

The fluids in a confined space exert pressure in which direction?

  1. Upward

  2. Downward

  3. Forward

  4. All directions


Correct Option: D
Explanation:

Pascal's law or the principle of transmission of fluid-pressure is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same.

so option ( D) would be correct

Fill in the blank.

Liquids exerts pressure in _______ directions.

  1. One

  2. Two

  3. All

  4. It do not extent any pressure


Correct Option: C
Explanation:

Like solids fluids (liquids and gases) also exent pressure. A solid exent pressure only in the downward direction due to its weight, whereas liquids and gases exent pressure on the walls of their container.

If a sweet water fish enters a sea, the fish will

  1. swell

  2. be squeezed

  3. remain as it is

  4. suffer none of these


Correct Option: B
Explanation:

Liquid pressure is given by =$\rho \times g \times h$

The water from river has a lower density than the sea water. So, at equal depth, sweet water or river water exerts less pressure than sea water. Body of a sweet water fish is habituated with this lower pressure of river water. Naturally, when the fish will enter the sea, it will suffer greater pressure due to increase in density and hence the body of the fish will be squeezed slightly.

There are two fish tanks each of depth $0.5 m$. Base area of one is $0.5m^2$ and that of another is $0.1m^2$. At the depth of which tank will a fish feel larger pressure?

  1. The tank of wider base area

  2. The tank of smaller base area

  3. Equal for both tanks

  4. Can't say


Correct Option: C
Explanation:

Liquid pressure is given by =$ \rho \times g \times h$
Liquid pressure depends on the depth and not on surface area. Both the tanks have the same depth. So, for both the tanks, the fish will feel equal pressure.

Fluids are
  1. The substances which are lighter than air.
  2. The substances which let substances float on them.
  3. The substances which can flow easily.
  4. Liquids.


Correct Option: C
Explanation:

A fluid is a substance such as liquid or gas which can flow easily, has no fixed shape and can changes its shape at a steady rate when acted upon by a force tending to change its shape.

If a sea fish enters a river, the fish will

  1. swell

  2. be squeezed

  3. remain as it is

  4. suffer none of these


Correct Option: A
Explanation:

Density of sea water is more than that of river water. So, at same depth, sea water exerts greater pressure. And, the body of the sea fish is habituated with the high pressure from outside. Now, as the same fish enters the river, water density being low, will suffer less pressure from outside. As a result, the body of the fish will swell out slightly.

Pressure exerted at a point in a liquid is 

  1. scaler

  2. vector

  3. teasor

  4. none


Correct Option: A
Explanation:

Pressure exerted at a point in a liquid is equal in magnitude in all directions, hence it is scalar.

Pressure exented by the liquids on the walls of the container depends upon

  1. density

  2. declaration due to gravity

  3. height of the liquids column

  4. all


Correct Option: D
Explanation:

Pressure exerted by the fluids on the sides of the container is called lateral pressure. It depends on the all the given options, mathematically p = hpg

Mark the most common fluids
  1. Air

  2. Water

  3. Kerosene

  4. Both A and B are considered as most common fluids

Correct Option: D
Explanation:
A fluid is a substance such as liquid or gas which can flow easily, has no fixed shape and can changes its shape when acted upon by a force tending to change its shape.
Air is the most common mixture of gas.
Water is the most common liquid present on earth.
Hence correct answer is option D.
Mark the correct Statements.
  1. Solids exert pressure on a surface due to their own weight.
  2. Fluids also have weight.

  3. Liquids can exert pressure.

  4. All the above


Correct Option: D
Explanation:

A fluid is a substance that has no fixed shape, can flow easily and yields easily to external pressure, e.g., a gas or  a liquid.

Pressure is exerted by fluids because of their weight. Static fluid pressure is given by = $\rho \times g \times h $
where $h$ =  depth of the fluid, 
            $\rho$ =  density of the fluid and 
            $g$ = the acceleration due to gravity.
Well knowingly, the solids exert pressure on the surface on which they are placed, given by $P=\dfrac{mg}{A}$
Hence correct answer is option D.

Fluids exert pressure on
  1. Air

  2. The container in which they are stored
  3. Both A and B

  4. Their own molecules which are present on the surface of the container

Correct Option: B
Explanation:
A fluid is a substance that has no fixed shape and yields easily to external pressure; a gas or  a liquid.
Pressure is exerted by fluids because of their weight. 
Static fluid pressure is given as = $\rho \times g \times h$
where $h$ = depth of the fluid,
           $\rho$ = the density of the fluid and
           $g$ = the acceleration of gravity.
Hence they exert pressure in the container in which they are stored.

How fluid pressure is different from solid pressure?

  1. Solid pressure leads to deformity while fluid pressure doesnt

  2. Solid pressure doesn't lead to deformity while fluid pressure leads to deformity

  3. Both leads to deformity

  4. Both doesn't lead to deformity


Correct Option: A
Explanation:

Solid pressure is different from fluid pressure in the sense that solid pressure leads to deformity while fluid pressure doesnt.

State True or False.
A fluid exerts pressure in all possible directions.

  1. True

  2. False


Correct Option: A
Explanation:

Since a fluid has no definite shape, its pressure applies in all directions. Fluid pressure can also be amplified through hydraulic mechanisms and changes with the velocity of the fluid.

The size of an air bubble rising up in water.

  1. Decreases

  2. Increases

  3. Remains same

  4. May increase or decrease


Correct Option: B
Explanation:

 As the pressure exerted by water is directly proportional to the depth of water, as the depth of water increases in a water body, the pressure increases linearly. So when a air bubble rises in water, the pressure acting on the air bubble decreases. 


We know the that as the the pressure acting on gas is inversely proportional to the volume occupied by it i.e. if the pressure increases, then the volume occupied will decrease and if the pressure acting on the gas decreases, then the volume occupied by by the gas will increase.


In the rising air bubble, as the pressure is decreasing, the volume and hence its size increases.

so option (B) is correct.

Pressure inside an inflated balloon is

  1. Less than atmospheric pressure

  2. Greater than atmospheric pressure

  3. Equal to atmospheric pressure

  4. May be less than or equal to atmospheric pressure


Correct Option: C

The pressure in an enclosed fluid is transmitted _________ in all directions with diminished force

  1. equally

  2. unequally

  3. cant say

  4. none


Correct Option: A
Explanation:
According to Pascal's law: Pressure in an enclosed fluid is transmitted equally in all direction with diminished force at all the points with same depth. 

Different liquids exert the _____ pressure at a given depth. 

  1. same

  2. different

  3. can't say

  4. none


Correct Option: B
Explanation:

Different liquids will exert the different pressure at a given depth because of difference in their density.

Liquid rise in a syringe when its piston is pulled up due to 

  1. Atmospheric pressure

  2. Inertia of motion

  3. Inertia of rest

  4. Conservation of momentum


Correct Option: A
Explanation:

When the piston is pulled up, air pressure inside syringe reduces because of increase in volume. While pressure outside syringe is more than that. So, it pushes liquid into syringe.

Based on which of the following does a water pump draw water?

  1. Pressure difference

  2. Bernoulli's principle 

  3. Law of Gravity

  4. None of these


Correct Option: A
Explanation:

Water pump reduses the pressure at one end of the pipe and pressure difference drives the water to come up from well.

What is the relationship between liquid pressure and the depth of a liquid?

  1. Directly proportional

  2. Inversely proportional

  3. Linear

  4. None of these


Correct Option: A
Explanation:

The relationship between liquid pressure and the depth of a liquid:

Pressure at depth 'h' = density of fluid $\times $ acceleration due to gravity 'g' $\times $  depth 'h'.
Pressure is directly proportional to depth. If we triple the depth, we triple the pressure.

The pressure a liquids exerts against the sides and bottom of a container depends on the 

  1. atmospheric pressure

  2. surface area

  3. volume of container

  4. density and depth of liquid


Correct Option: D
Explanation:

$\because p = h\times d\times g$
where, p = pressure, h = depth (height), d = density,  g = acceleration due to gravity = constant.

So, pressure depends on density and depth of liquid.

A tank $5\ m$ high is half filled with water and then is filled to the top with oil of density $0.85\ g\ cm^{-3}$. The pressure at the bottom of the tank, due to these liquids, is

  1. $1.85\ g$

  2. $89.25\ g\ dyne\ cm^{-3}$

  3. $462.5\ g\ dyne\ cm^{-2}$

  4. $500\ g\ dyne\ cm^{-2}$


Correct Option: C
Explanation:

We know that the pressure increases as we go deep into a liquid. The relation is given by $\Delta P = \rho g\Delta h$


Given that the tank is half filled with water and half with oil.
Thus, $h _\textrm{oil} = 2.5\textrm{ m}$ and $h _\textrm{water} = 2.5\textrm{ m}$

Thus, pressure at the bottom of the tank is $\Delta P = \Delta P _\textrm{oil} + \Delta P _\textrm{water} = 0.85\times 250g + 1\times 250g=462.5g \textrm{ dyne cm}^{-2}$

A barometer which measures atmospheric pressure more accurately is ..........

  1. Fortin's barometer

  2. mercury barometer

  3. anaeroid barometer

  4. Torricelli barometer


Correct Option: B
Explanation:

A barometer which measures atmospheric pressure most accurately is mercury barometer.

Hence, option B is correct.

The Pressure at any point in the liquid is proportional to :

  1. The density of liquid.

  2. The depth of point below the surface.

  3. The acceleration due to gravity.

  4. All the above


Correct Option: D
Explanation:

Pressure at any point in the liquid $(P)=hdg$
i.e., $P\alpha h$
(depth of point below the surface)
$\alpha d$ (density of liquid)
$\alpha g$ (acceleration due to gravity)

Liquid pressure at a point in a liquid does not depend on the :

  1. Density of liquid

  2. Shape of the vessel in which the liquid is kept

  3. Depth of the point from the surface

  4. Acceleration due to gravity


Correct Option: B
Explanation:

pressure in a fluid = $\rho gh $ 

so clearly it is independent of the shape of the vessel in which the liquid is kept .
hence option (B) is correct .

Which of the following scientists invented mercury barometer?

  1. Blaise Pascal

  2. Evangelist Torricelli

  3. Robert Brown

  4. Amedeo Avogadro


Correct Option: B
Explanation:

Mercury Barometer was invented by Evangelist Torricelli in the year 1643. It is a device used to measure atmospheric pressure.

A fluid exerts pressure in all possible directions of a container.

  1. True

  2. False


Correct Option: A
Explanation:

this is the property of fluid to exert pressure in all directions of a container.

so option (A) is correct

Pressure at a point inside the liquid does not depend upon :

  1. The depth of the point below the surface of the liquid.

  2. The nature of the liquid.

  3. The acceleration due to gravity at that point.

  4. The shape of the container.


Correct Option: D
Explanation:

Pressure at a point inside the liquid $(P)=hdg$
Hence, it depends on the depth of the point below the surface of the liquid the acceleration due to gravity at that point and on the nature of the liquid but not on the shape of the containing liquid.

Extremely small pollen grains in water are viewed through a microscope. The grains are seen to
move continually and randomly.
What is the reason for this random movement?

  1. The grains are moved by randomly moving water molecules

  2. The grains are moved by random convection currents in the water

  3. The grains are moved by random rays of light reflecting off them

  4. The grains are moved by the random motion of their own atoms


Correct Option: A
Explanation:

This is due to brownian motion of fluid particles. The pollen get hitted by the water molecules and carried away by them. 

This is reason behind the random motion of pollen grains in water .

A hose shoots water straight up to a height of $2.5m$. The opening end of the hose an area of $0.75\ cm^{2}$. How much water will come out in one minute ?

  1. $21.5\ litre$

  2. $25\ litre$

  3. $30\ litre$

  4. $31.5\ litre$


Correct Option: A

The deep sea divers wear specially designed suites to protect from

  1. different sea organisms

  2. different sea plants

  3. high water pressure

  4. none


Correct Option: C
Explanation:

To be able to bear very high pressure of liquid in deep sea.

Fill in the blank spaces by choosing the correct words from the options given below.

The hulls of the______are made very strong to withstand huge pressure exerted by the sea water. 

  1. $liquids$

  2. $gases$

  3. $submarines$

  4. All of the above


Correct Option: C
Explanation:

Submarines.
The hull of Submarines are specially Strengthened to prevent it from collapsing from the high pressure of the water outside while submerged. Roughly every $30$ feet of depth under water adds another atmosphere of inward pressure on the hull.

A deep sea diver may hurt his ear drum during diving because of:

  1. lack of oxygen

  2. more atm pressure

  3. more water pressure

  4. all of the above


Correct Option: C
Explanation:

The pressure at a depth $h$ below the surface of water is given by 

$P=P _0+h\rho g$
Hence as the depth increases, the pressure increases.
Due to this increased pressure, as the diver goes deeper in sea water, the ear drum may get damaged.

In cities water supply from an overhead tank to.the houses is done due to:

  1. difference in pressure

  2. gravitational force

  3. decrease of friction in pipes

  4. flow of liquid


Correct Option: B
Explanation:

The water in an overhead tank has higher gravitational potential to compared to water which finally flows out of the taps in the houses. 
The water moves due to this decrease in gravitational potential energy of water by flowing out of taps, or, the water is supplied by the gravitational force acting on water.

Fluids include

a) Solids    
b) Liquids  
c) Gases

  1. a and b

  2. b and c

  3. a and c

  4. All the above


Correct Option: B
Explanation:

A fluid is a substance that has no fixed shape and yields easily to external pressure; a gas or  a liquid, or, which can easily flow.

It is due to this property of variation of pressure along a fluid that it exerts a buoyant force on a body placed inside it. 

What is the difference between the pressure on the water surface and that on the bottom?

  1. $\rho gh$

  2. $\frac{\rho g}{h}$

  3. Zero

  4. Infinity


Correct Option: A
Explanation:

The pressure at the bottom of the water surface is

$P=\dfrac{F}{A}=\dfrac{W}{A}=\dfrac{Ah\rho g}{A}=\rho gh$

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