 ### Pressure - class-IX

 Description: pressure Number of Questions: 50 Created by: Vinaya Modi Tags: statics and dynamics of fluid (liquid and gas) pressure in liquids and gases properties of matter floatation forces and matter physics force pressure motion, force and pressure
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As the depth of a liquid increases, the pressure of liquid decreases.

1. True

2. False

Correct Option: B
Explanation:

pressure at a point in a fluid is = $\rho gh$ where $\rho$ is the density of the liquid , h is the height or depth of the object from the surface , so pressure increases with increase in depth so given statement is false .

hence option (B) is correct .

76 cm of Hg pressure is equivalent to 76 pascal.

1. True

2. False

Correct Option: B
Explanation:

1 atm = 1 pa = 76 cm of Hg

hence given statement is false so option (B) is correct

Sideways pressure exerted by a liquid is called its lateral pressure.

1. True

2. False

Correct Option: A
Explanation:

Pressure exerted sideways is known as  lateral pressure  , hence the given statement is true so option (A) is correct

With the increase in the weight of an object the pressure:

1. Increases

2. Decreases

3. Is not affected

4. None of these

Correct Option: A
Explanation:

With the increase in the weight of an object the pressure increases because pressure is thrust per unit area.

The area of cross-section of the pump plunger and the press plunger of hydraulic press are $0.03 m^2$ and $9 m^2$ respectively. How much is the force acting on the pump plunger of the hydraulic press overcomes a load of 900 kgf?

1. 2 kgf

2. 3 kgf

3. 4 kgf

4. 5 kgf

Correct Option: B
Explanation:

$Load=900 kgf, Effort (E)=?$
Area of cross section of the press plunger $=a _1=9 m^2$
Area of cross - section of the pump plunger $=a _2=0.03 m^2$
By Pascal's law,
Pressure exerted by pump plunger $=$ pressure exerted on press plunger.
i.e., $\displaystyle \frac {L}{E}=\frac {a _1}{a _2}\Rightarrow \frac {900 kgf}{E}=\frac {9 m^2}{0.03 m^2}$
$\displaystyle \Rightarrow E=\frac {900 kgf\times 0.03 m^2}{9 m^2}=3 kgf$.

Force exerted by a truck is 500000 N and the pressure on the ground is 2500000 Pa. Calculate the area of contact of tyres with ground?

1. $0.1m^2$

2. $0.2m^2$

3. $0.3m^2$

4. $0.4m^2$

Correct Option: B
Explanation:

Force $(F)=500000 N$
$Pressure=250000 Pa, Area (A)=?$
$A=\frac {F}{P}=\frac {500000}{2500000}m^2=0.2m^2$.

Deep sea divers put on special suit to :

1. Maintain their body temperature in cold sea water

2. Protect against sea animals

3. Maintain pressure

4. Keep them dry

Correct Option: C
Explanation:

To maintain normal atmospheric pressure below sealevel, deep seadivers wear a special suit.

Which of the following quantity is expressed as force per unit area?

1. Work

2. Pressure

3. Volume

4. Area

Correct Option: B
Explanation:

Pressure is expressed as force per unit area

Pressure is vector quantity .State true or false.

1. True

2. False

Correct Option: B
Explanation:

Pressure is a scalar quantity, not a vector quantity. It has a magnitude but no direction associated with it. Pressure acts in all directions at a point inside a gas. At the surface of a gas, the pressure force acts perpendicular to the surface.

For example. one that does not appear to move or flow. While the gas as a whole does not appear to move, the individual molecules of the gas, which we cannot see, are in constant random motion. Because we are dealing with a nearly infinite number of molecules and because the motion of the individual molecules is random in every direction, we do not detect any motion. If we enclose the gas within a container, we detect a pressure in the gas from the molecules colliding with the walls of our container. We can put the walls of our container anywhere inside the gas, and the force per area (the pressure) is the same. We can shrink the size of our "container" down to an infinitely small point, and the pressure has a single value at that point.

Therefore, it is false.

Two stretched remembrance of area $2$ and $3\ m^{2}$ are placed in a liquid at the same depth. The ratio of the pressure on them is

1. $1:1$

2. $2:3$

3. $\sqrt {2}:\sqrt {3}$

4. $2^{2}:3^{2}$

Correct Option: A

A Liquid of density p is coming out of a hosepipe of the radius with horizontal speed $\upsilon$  and hits a mesh.  50 % of the liquid passes through the mesh unaffected.  25 % loses all of its momentum and 25 % comes back with the same speed.  The resultant pressure on the mesh will be:

1. $\frac{3}{4}p\upsilon ^{2}$

2. $p\upsilon ^{2}$

3. $\frac{1}{2}p\upsilon ^{2}$

4. $\frac{1}{4}p\upsilon ^{2}$

Correct Option: A

Since pressure is force per unit area, it is a vector quantity.

1. True

2. False

3. Ambiguous

4. Data insufficient

Correct Option: B
Explanation:

Pressure is defined as force per unit area. It is usually more convenient to use pressure rather than force to describe the influences upon fluid behavior. The standard unit for pressure is the Pascal, which is a Newton per square meter.
Therefore, pressure is a scalar quantity, not a vector quantity. It has magnitude but no direction sense associated with it. Pressure acts in all directions at a point inside.
Hence, the statement is false.

We sit in the room with windows open. Then

1. Air pressure on the floor of the room equals the atmospheric pressure but the air pressure on the ceiling is negligible

2. Air pressure is nearly the same on the floor, the walls and ceiling

3. Air pressure on the floor equals the weight of the air column inside the room (from floor to ceiling) per unit area

4. Air pressure on the walls is zero since the weight of air acts downward

Correct Option: B
Explanation:

Varying air pressures in buildings result from uncontrolled air flow patterns.When a space is under a positive air pressure, indoor air will be pushed outward in the walls, floor and ceiling. When a space is under a negative pressure, air will be pulled inward through the walls, floor and ceiling.
In this case, the windows in the room are open and so there is free flow of air in and out of the room.
Hence, air pressure is nearly the same on the floor, the walls and ceiling.

In a hydel station, the motion produced in turbines is due to the

1. burning of coal

2. burning of diesel

3. flow of water

4. production of steam

Correct Option: C
Explanation:

Water flowing in the river is comprised of kinetic energy and potential energy. In hydroelectric power plants the potential energy of water is utilized to produce electricity.

The dam is the most important component of hydroelectric power plant. The dam is built on a large river that has abundant quantity of water throughout the year. It should be built at a location where the height of the river is sufficient to get the maximum possible potential energy from water.

Pascal is a unit used for measuring :

1. buoyant force

2. thrust

3. pressure

4. none of these

Correct Option: C
Explanation:

Pascal is the S.I. unit of pressure. So, the pressure is measured in the unit pascal.

Pressure acting on a body is a :

1. scalar quantity

2. vector quantity

3. slanted force

4. all the above are wrong

Correct Option: A
Explanation:

pressure is a scalar quantoty as it does not have any direction.

$1$  millibar is equal to

1. $100 N {m}^{-2}$

2. $10 N {m}^{-2}$

3. $1 N {m}^{-2}$

4. $\displaystyle\frac{1}{100} N {m}^{-2}$

Correct Option: A
Explanation:

1 millibar = $10^{-3} bar$

and 1 bar = $10^5$ pa
hence 1 millibar = 100 pa = 100n$m^{-2}$

Pascal is the unit for

1. Pressure

2. Thrust

3. Buoyant force

4. None of these

Correct Option: A
Explanation:

pascal is the SI unit of pressure

so option (A) is correct

$Pressure \times Volume=$

1. $Work$

2. $Force$

3. $Acceleration$

4. None of these

Correct Option: A
Explanation:

$Pressure=\dfrac{Force}{Area}=\dfrac{Force \times Distance}{Area \times Distance}=\dfrac{Work}{Volume}$

So, $Pressure \times Volume=Work$

Fill in the blank.

On increasing force, the pressure____________.

1. increases

2. decreases

3. remains constant

4. may increase or decrease

Correct Option: A
Explanation:

$Pressure=\dfrac{Force}{Area}$

So, on increasing force, pressure increases.

Which of the following describe $Pressure$ correctly?

1. $Pressure=\dfrac{Work}{Volume}$

2. $Pressure=Work \times Volume$

3. $Pressure=\dfrac{Force}{Volume}$

4. None of these

Correct Option: A
Explanation:

$Pressure=\frac{Force}{Area}=\frac{Force \times Distance}{Area \times Distance}=\frac{Work}{Volume}$

Unit of Pressure is a

1. direct unit

2. derived unit

3. complex unit

4. none of these

Correct Option: B
Explanation:

Unit of Pressure, $Pa$ (in SI) is derived from the units of Force ($N$ in SI) and Area ($m^2$ in SI).
$Pa=\dfrac{N}{m^2}$
So, it is a derived unit.

For constant $Pressure$

1. $Force \propto Area$

2. $Force \propto \frac{1}{Area}$

3. $Force \propto Area^2$

4. None of these

Correct Option: A
Explanation:

$Pressure=\dfrac{Force}{Area}=Constant$

$\therefore$ $Force=Constant \times Area$

Or, $Force \propto Area$

When the temperature of atmosphere rises,

1. Density of air increases.

2. Atmospheric pressure decreases.

3. Both A and B.

4. None

Correct Option: B
Explanation:

With the increase in temperature, the density of atmosphere decreases, hence the atmospheric pressure decreases.

Fill in the blank.

Pressure is the force acting _________ on a unit area of object

1. Perpendicularly

2. Parallel

3. Diagonally

4. All

Correct Option: A
Explanation:

Pressure is defined as force per unit area. The standard unit for pressure is the Pascal, which is a Newton per square meter.

$P=\dfrac{F}{A}$

Here the force acts perpendicularly on the area.

As the moisture present in the air increases,

1. Density if air increases.

2. Atmospheric pressure decreases.

3. Both A and B

4. None

Correct Option: B
Explanation:
The increased moisture in density suggests the decrease in its density and hence the atmospheric pressure also decreases.

Effect of a force depends on the

1. Volume of the object on which the force acts

2. Area of the object on which the force acts

3. Displacement caused by the force

4. None

Correct Option: B
Explanation:

Pressure is a measure of effect of force on an object.

Pressure is defined as force per unit area, that is,
$P=\dfrac{F}{A}$
Hence the effect of force depends upon the area upon which it acts. Smaller area would have greater effect for equal amount of applied force.

Pressure exerted on a surface depends on
1. Thrust

2. Area on which thrust is applied.

3. Both A and B

4. None

Correct Option: C
Explanation:

Pressure can be defined as force per unit area i.e. $\dfrac{Force}{Area}$.

Hence pressure is depends on thrust (force) and the area on which the force acts (area on which thrust is applied)

As altitude increases, atmospheric pressure

1. increases.

2. decreases.

3. remains constant.

4. None.

Correct Option: B
Explanation:

The atmospheric pressure exists due to weight of the atmosphere above it.
As the altitude increases, the amount of atmosphere above, and hence its weight, and hence the atmospheric pressure decreases.

Which of the following ratio expresses pressure?

1. Force/area

2. Energy/volume

3. Energy/area

4. Force/volume

Correct Option: A
Explanation:

We know that pressure is the force per unit area.

So pressure $=force/area$

1000 small balls each weighing 1 g strike one sq. cm of a area per second with a velocity of 100 m/sec in a normal direction and rebound with the same velocity. The pressure on the surface (in N/m$^2$) is :

1. $2 \times 10^3$

2. $4 \times 10^6$

3. $10^7$

4. $2 \times 10^6$

Correct Option: D

Identify the following shows the application of pressure in our everyday life?

1. The blade of Ice-skating shoe is very sharp.

2. It is easier to drive a sharp tipped nail into wood.

3. Sharp knife cuts better.

4. Foundation of high-rise building are kept narrow.

Correct Option: A,B,C,D
Explanation:

(A) if we decrease the area of the ice skating blades, then we mean to say we are increasing the pressure. We actually do this to increase pressure which reduces the chances of getting slipped.

(B) same concept is applicable in this as it was in the option (a). sharp tipped nail is having less area  and therefore exerts more pressure when it is tipped. so it easily gets tipped into the wood or even into the walls.
(C) same concept is in this option as well.
(D) same concept as it was in the previous 3 options.

Choose the correct statement from the following?

1. Pressure is same at all points in the horizontal plane.

2. A liquid seeks its own level.

3. The lateral pressure exerted by a liquid decreases with the increase in depth of the liquid.

4. The upper surface of a stationary liquid is always horizontal.

Correct Option: A,B,D
Explanation:

(a) Pressure is same at all points in the horizontal plane. (correct)
(b) A liquid seeks its own level. (correct)
(c) The lateral pressure exerted by a liquid decreases with the increase in depth of the liquid. (wrong)
(d) The upper surface of a stationary liquid is always horizontal. (correct)

For the equlibrium AB (g) $\rightleftharpoons A (g) + B(g). K _p$ is equal to four times the total pressure. Calculate the number moles of A formed if one mol of AB is taken initially

1. 0.45

2. 0.30

3. 0.60

4. 0.90

Correct Option: D

A same amount of same gas of temperature T are enclosed in a three identical vessel A,B, & C. The temperature of wall of three container is $T _A , T _B$ & $T _C (T _A > T _B > T _C)$ respectively. The pressure on wall of vessel.

1. $P _A > P _B > P _C$

2. $P _A < P _B < P _C$

3. $P _A = P _B = P _C$

4. Deta's are insufficient to decide.

Correct Option: A
Explanation:

$\begin{array}{l} PV=nRT \ P\propto T \ \therefore \, { T _{ A } }>{ T _{ B } }>{ T _{ C } } \ So, \ { P _{ A } }>{ P _{ B } }>{ P _{ C } } \ Hence, \ option\, \, A\, \, iscorrect\, answer. \end{array}$

A hole is made at the bottom of a tank filled with water. If total pressure at the bottom of the tank is three atmosphere, then the velocity of efflux at the bottom is (1 atm = $10^5 N/m^2$)

1. $\sqrt{400} m/s$

2. $\sqrt{200} m/s$

3. $\sqrt{600} m/s$

4. $\sqrt{500} m/s$

Correct Option: A
Explanation:

Given,

$\begin{array}{l} P=1000kg/{ m^{ 3 } } \ P=3atm=3\times { 10^{ 5 } }N/{ m^{ 2 } } \ { P _{ 0 } }=1atm={ 10^{ 5 } }N/{ m^{ 2 } } \end{array}$
Pressure due to liquid column is
$P - {P _0} =\rho gh$
velocity of flux $V = \sqrt {2gh}$
$\begin{array}{l} V=\sqrt { 2\dfrac { { \left( { p-{ P _{ 0 } } } \right) } }{ \rho } } \ =\sqrt { \dfrac { { 2\left( { 3\times { { 10 }^{ 5 } }-{ { 10 }^{ 5 } } } \right) } }{ { 1000 } } } \ =\sqrt { \dfrac { { 4\times { { 10 }^{ 5 } } } }{ { 1000 } } } \ =\sqrt { 400 } m/s \end{array}$
Hence,
option $A$ is correct answer.

$3$ moles of a monoatomic gas requires $60\ cal$ heat for $5^{\circ}C$ rise of temperature at constant volume, then heat required for $5$ moles of same gas under constant pressure for $10^{\circ}C$ rise of temperature is $(R = 2\ cal/mole-k)$.

1. $200\ cal$

2. $400\ cal$

3. $100\ cal$

4. $300\ cal$

Correct Option: C

Temperature of $1\ mole$ of a gas is increased by $2^ {o}C$ at constant pressure, work done is

1. $R$

2. $2R$

3. $R/2$

4. $3R$

Correct Option: B
Explanation:

$W = nR\Delta T$

$= 1\,molRJ\,{K^{ - 1}}\,mo{l^{ - 1}}\,2K$
$= 2R\,\,joules$
Hence,
option $(B)$ is correct answer.

Air is pumped into an automobile tube upto a pressure of $200 \mathrm{kP}$ in the morning when the air temperature is $22^{\circ} \mathrm{C}$ . During the day, temperature rises to $42^{\circ} \mathrm{C}$ and the tube expands by $2 \%$ . The pressure of the air in the tube at this temperature, will be approximately

1. $212 \mathrm{kPa}$

2. $209 k P a$

3. $206 \mathrm{kPa}$

4. $200 \mathrm{kPa}$

Correct Option: B
Explanation:

$\begin{array}{l} Given\, \, { P _{ 1 } }=200\, \, k\, pa \ { T _{ 1 } }=22^{ \circ }C=273+22-295K \ { T _{ 2 } }=42^{ \circ }C=273+42=315K \ PV=nRT \ \left( { \dfrac { { PV } }{ T } } \right) ={ { constant } }\left[ \begin{array}{l} { { Since } }\, \, number\, \, of\, \, moles \ and\, \, R\, \, are\, \, { { constant } } \end{array} \right] \ \dfrac { { { P _{ 1 } }{ V _{ 1 } } } }{ { { T _{ 1 } } } } =\dfrac { { { P _{ 2 } }{ V _{ 2 } } } }{ { { T _{ 2 } } } } \ \dfrac { { 200\times 1 } }{ { 295 } } =\dfrac { { { P _{ 2 } }\left( { 1.02 } \right) } }{ { 315 } } \ { P _{ 2 } }=\dfrac { { 200\times 315 } }{ { 295\times 1.02 } } \, \, kPa \ = 209\, \, kPa \end{array}$

Option B.

A person blows into open-end of a long pipe. As a result, a high pressure pulse of air travels down the pipe. When this pulse reaches the other end of the pipe,

1. a high pressure pulse starts traveling up the pipe, it the other end of the pipe is open.

2. a low pressure pulse starts traveling up the pipe, if the other end of the pipe is open.

3. a low pressure pulse starts traveling up the pipe, if the other end ot the pipe is closed.

4. a high pressure pulse starts traveling up the pipe, if the other end of the pipe is closed.

Correct Option: D
Explanation:

A pressure wave undergoes a phase change of $\pi$ radians on

reflection from open end of no phase change occurs on reflection from
closed end.

Which of the following are units used to measure pressure?

1. $kg$ ${m}^{-2}$

2. pascal (Pa)

3. newton per ${m}^{2}$

4. joules

Correct Option: B,C
Explanation:

The pressure is the force per unit area. So, $P=F/A$

The unit of force is newton (N) and unit of area is $m^2$.
Thus, the unit of pressure is $N/m^2$.
Pascal is the SI unit of pressure. It is equal to one newton divided by one square meter.

The SI unit of pressure is $N/m^2$.This unit is otherwise called ____________.

1. Pascal

2. Newton

3. Joule

4. None of these

Correct Option: A
Explanation:

Pressure is defined as force applied per unit area. Hence, its SI unit is $N/{ m }^{ 2 }$ or Pascal here,

1 Pascal = 1 $N/{ m }^{ 2 }$.

Two women are of the same weight. One wears sandals with pointed heels while the other wears sandals with flat soles. Which one would feel more comfortable while walking on a sandy beach?

1. The one with pointed heels

2. The one with flat soles

3. Both will feel similar comfort

4. Can't say

Correct Option: B
Explanation:

Pressure(P)$=$$\frac{Force(F)}{Area(A)}$

As both the women have same weight, so both of them will apply the same force on the ground. But flat soles having larger area compared to sandals with pointed heels, will exert lesser pressure compared to that of sandals having pointed heels. So, the sandals with pointed heels will sink more. Therefore, the woman having flat sole sandal will feel more comfortable while walking on a sandy beach.

Force acting per unit area is

1. Acceleration

2. Pressure

3. Velocity

4. None

Correct Option: B
Explanation:

Pressure is defined as force per unit area. The standard unit for pressure is the Pascal, which is a Newton per square meter.

$P=\dfrac{F}{A}$

For an object sitting on a surface, the force pressing on the surface is the weight of the object, but in different orientations it might have a different area in contact with the surface and therefore exert a different pressure.

The pressure of the fluid acting sideways is known as its lateral pressure

1. True

2. False

Correct Option: A
Explanation:

pressure acting sideways is known as lateral pressure .

so option (A) is correct

Pressure is equal to

1. $\dfrac{Force}{Area}$

2. $\dfrac{Area}{Force}$

3. $\dfrac{Thrust}{Area}$

4. $\dfrac{Area}{Time}$

Correct Option: A
Explanation:

Pressure can be defined as the force per unit area which can be written as $\dfrac{Force}{Area}$.

Fill in the blank.

Pressure is a __________ quantity.

1. Scalar

2. Vector

3. both A and B

4. neither A nor B

Correct Option: A
Explanation:

Although Force and Area, both are vector quantities, pressure is a scalar quantity.

What is the relation between thrust and pressure?

1. Pressure directly proportional to thrust

2. Pressure indirectly proportional to thrust

3. No relation

4. none

Correct Option: A
Explanation:
Hence pressure=$P=\dfrac{Thrust}{Area}$
$\implies Pressure\propto Thrust$

Thrust is which type of force:

1. Parallel

2. Perpendicular

3. normal

4. Both b and c

Correct Option: D
Explanation:

The force which is perpendicular to the surface on which it is acted is called a thrust.

A perpendicular force is also called 'normal' to that surface.
Hence correct answer is option D.

Which Newton's laws describe thrust?

1. First and second

2. second and third

3. only second

4. first and third

Correct Option: B
Explanation:

Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction on that system.

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