Science note1)      Define pressure and write its SI Unit?

Ans:  Force acting perpendicularly per unit area is called pressure. Its SI unit is pascal (Pa) i.e. Nm-2

2)      Name two factors that affect pressure.

Ans:  The two factors affecting pressure are;

·         Force

·         Area

Mathematically; Pressure (p) =

3)      What relation does exist between pressure and area?

Ans:  Pressure is inversely proportional to Area (A)

i.e. P µ

4)      It is easier to cut the things by using a sharp knife than by using a blunt one. Why?

Ans: The edge of sharp knife has less surface area than that of blunt one. hence, it exerts more pressure on the thing to be cut. Since, pressure is inversely

Proportional to Area . Therefore, it is easier

to cut things by suing a sharp knife than by using a blunt one.

5)      The shoes of football players are provided with studs. Why?

Ans:  Studs reduce the surface area of contact between shoes and ground. Hence, more pressure is applied to the ground and players can run safely without slipping on the ground. Since, pressure µ

6)      The foundation of the building is made wider than the walls. Why?

Ans:  The foundation of the building is made wider than the walls of a building because walls and its roof exert pressure on the wide area of the foundation and this reduces pressure over the earths surface and the building is saved from collapsing. Since, pressure µ

7)      Camel can walk on the desert but not the horse. Why?

Ans:  Camels are provided with flat hoofs. These flat hoofs exerts less pressure on the sand because pressure µ . But horse has narrow hoofs and exerts more pressure on the sand and sinks there. Thus camel can walk on the desert but not the horse.

8)      Tyres of tractors are wider than the tyres of cars. Why?

Ans:  Tractors are used in muddy areas. They must apply less pressure on the ground in order to run there. Hence, to decrease the pressure they apply, tyres of tractors are made wider. However, cars are often used in blacktopped road and that road can withhold more pressure. Hence, tyres of tractors are wider than that of cars.

9)      The backtyres of trucks are paired. Why?

Ans:  Pairing of tyres increases the area of contact of tyres with the ground and less pressure is exerted on the ground and to the tyres as well. This increases the life of tyres and helps the truck to run swiftly on the road without getting collapsed. Therefore, the backytres of trucks are paired.

10)    Write any two differences between thrust and pressure.

Ans:  The differences between thrust and pressure are as follows;

 Thrust (Force) Pressure a) It is an external agency that changes or tends to change the state of a matter from motion the rest and from rest motion. It is the force acting perpendicularly per unit area. b) Its SI unit is Newton (N) Its SI unit is pascal (pa) c) Mathematically Force (F)= mass (m) X acceleration (a) Mathematically, Pressure (p)=

11)    Mention three factor on which liquid pressure depends.

Ans:  Liquid pressure depends on the following factors;

i)                    Depth of liquid from the free surface (h)

ii)                  Density of liquid (d)

iii)                Acceleration due to gravity (g)

12)    The base of dam is mode wider than the top. Why?

Ans:  We know that the liquid pressure increases with the depth of the liquid. Hence, water in dam exerts more pressure at the bottom than at the top. To overcome that pressure, the base of dam is made wider.

13)    Deep sea divers need swim suit. Why?

Ans:  Since, liquid pressure is directly proportional to the depth of the liquid. Sea divers reach to the deep part of the sea where the liquid pressure is excessively high. Hence to overcome that pressure, deep sea divers need swim suit.

14)    Two identical tanks are filled with water and mercury respectively. On which tank more pressure is experienced at the bottom?

Ans:  The tank filled with mercury will experience more pressure at its base.

Since, liquid pressure directly proportional to the density of the liquid at constant depth and acceleration due to gracility. Density of mercury is more than that of the water. Hence tank filled with mercury will experience more pressure at its base.

15)    The bucket at the bottom floor fills faster than at the top floor from the identical taps. Why?

Ans:  The depth of water column to the bottom floor is more than the depth to the top floor. Hence, water from the tap of bottom floor comes with greater pressure to fill the bucket fester than at the top floor. As liquid pressure is directly proportional to the depth of the liquid i.e. P µ h at constant density and acceleration due to gravity.

16)    The blood pressure in human body is grater at feet than at the brain. Why?

Ans:  Since, the depth of feet from the heart is more than the depth of the brain. As liquid pressure is directly proportional to the depth of the liquid column, blood exerts more pressure at feet.

17)    A tank filled with water is brought from himalyan region to Terai region. What change in pressure is seen at the bottom of the tank? Why?

Ans:  The pressure exerted at the bottom of the tanks will be more in Terai region. The value of acceleration due to gravity is more in the terai region than that in the himalyan region. Since liquid pressure is directly proportional to the acceleration due to gravity at constant acceleration due to gravity deth of liquid so the pressure exerted by water will be more in Terai region.

18)    State Pascal's law.

Ans:  Pascal's law states that 'the external pressure applied on a liquid contained in a closed vessel is transmitted equally and perpendicularly in all the directions"

19)    Name any two device constructed on the basis of Pascal's law.

Ans:  The following devices are constructed on the basis of Pascal's law;

- Hydraulic        press

- Hydraulic        crane

- Hydraulic        brake

20)    On which property of the liquid Pascal's law is based?

Ans:  Pascal's law is based on the property of the liquid that the "liquid can not be compressed"

21)    What is up thrust? Write its SI unit?

Ans: The upward force exerted by the fluid on an object partially or wholly sinking it in it is called up thrust.

Its SI unit is Newton (N)

[up thrust is also called buoyant force]

22)    State Archimedes principle.

Ans:  According to Archimedes principle, "when a body is partially or wholly immersed in a liquid it experiences an up thrust which is equal to the weight of liquid displaced by the body"

23)    The weight of a body is less in water than in air. Why?

Ans:  Upthrust exerted by the fluid decreases the weight of an object immersed in it. Because of its higher density, the upthrust exerted by the air on an object. Hence the weight of a body is less in water in air.

24)    It is easier to swim in the sea than in the river. Why?

Ans:  it is easier to swim in the sea than in the river because the density of sea water is more than the density of river water. Hence the upthrust exerted by sea water on an object is more than the upthrust exerted by the river water.

25)    On which factor the upthrust depends?

Ans:  The upthrust depends upon the following factros;

i)                    Volume of the liquid displaced (v)

ii)                  Density of liquid  (d)

iii)                Acceleration due to gravity (g)

26)    A ship is so constructed that its external dimension is similar to that of an aeroplane will it fly in air?  Why?

Ans:  No, it won't fly in the air.

Because of less density of air the upthrust exerted by the air is much less than the upthrust exerted by water. This upthrust of air will not be sufficient to lift up the ship in the air.

27)    How does the plane fly?

Ans:  Due to the convex wings of plan, the air pressure above the wings is less and below the wing is more. Thus, this results the plane to fly up in the air as it is lifted up.

28)    The upthrust exerted by mercury is more than the upthrust exerted by water why?

Ans:  The density of mercury is more than that of water. Since upthrust is directly proportional to density i.e. U µ d. Hence the upthrust exerted by the mercury is more than that of water.

29)    What is density? Write its SI unit?

Ans:  Density is defined as mass per unit volume.

Its SI unit is kgm-3

30)    An egg sinks in pure water but floats on the concentrated salt solution. Why?

Ans:  An egg sinks in the pure water because its' density is greater than that of pure water. However, on egg floats on the salt solution because its density is less than that of salt solution.

31)    An iron nail sinks in water but floats on mercury. Why?

Ans: An iron nail sinks in water because its density is greater than that of water. However an iron nail floats on the mercury because its density is less than that of mercury.

32)    An ice cube flats on water. Why?

Ans:  An ice cube flats on water because its density is less than that of water and it can displace the water equal to its weight.

33)    What is relative density? Why it doesn't have any unit?

Ans:  Relative density is defined as the ratio of density of substance to the density of water at 4°c. It doesn't have any unit, because it is the simple ration of  the same physical quantities i.e.

34)    The relative density of mercury is 13.6. What do you mean by it?

Ans:  It means that mercury is 13.6 times denser tan water at 4°c i.e. for the same volume. Weight of mercury is 13.6 times more than the weight of water.

35)    What is specific gravity? Why doesn't it contain any unit?

Ans: Specific gravity is defined as the ratio of mass of certain volume of substance to the mass of same volume of water at 4°c.

It doesn't contain any unit because it is a simple ratio of same physical quantities.

36)    At which condition does a body float in water?

Ans:  A body floats in water in the following two conditions;

·         If the density of the body is less than the density of water

·         If the body can displace the water equal to its weight when place in water.

37)    State law of floatation.

Ans:  According to the law of floatation "A body floats in liquid if it can displace the liquid equal to its weight when place in that liquid"

38)    An iron nail sinks in water but the ship made by iron floats in it. Why?

Ans:  An iron nail can't displace the water equal to its weight, hence gets sink in water. However, the ship is so constructed that it can displace the water equal to its weight and can flat in water.

39)    Water change in floatation is seen when a cargo loaded ship travel from sea to the river?

Ans:  The density of river water is less than the density of sea water. Hence more volume of water is to be displaced on he river compared to the sea in order to maintain the weight of the water displaced equal to the weight of the ship. So, it sinks more in river than in sea.

40)    What is the difference in floating of empty ship and the cargo-loaded ship?

Ans:  In order to float in water ship must displace the water equal to its weight. Since the weight of empty ship is less than the weight of cargo loaded ship empty ship has to displace less than the weight of cargo loaded ship empty ship has to displace less amount of water and the cargo loaded ship has to displace more amount of water. hence, cargo loaded ship sinks more in water than the empty ship.

41)    What is hydrometer? On which principle is it based?

Ans:  Hydrometer is device that is used to measure the specific gravity and the density of a liquid.

Its is based on the law of floatation.

42)    The base of hydrometer is made heavier. Why?

Ans:  The base of hydrometer is made heavier in order to float vertically in liquid and to sink partially .

43)    The neck region of hydrometer is mode narrower. Why?

Ans: The neck region of hydrometer is made narrower for its grater sensitivity.

44)    What is lactometer?

Ans:  Lactometer is a device which is use to measure the purity of milk.

Q)     An iron nail sinks in water but the ship made by iron floats in water. Why?

Ans:  According to the law of flotation object floats in liquid if it can displace the liquid equal to its weight. At iron nail can't displace the water equal to its weight. Hence it gets sink in water however the ship is so constructed that it can displace the water equal to its weight and can float in water.

Prove that: P=hdg

Solution:

Let us consider, liquid of density (d) is kept in a vessel. Let h be the depth of the liquid column from the free surface.

Since,

Pressure (p)        =

or,     P                        =   [\F=m. g: where

m=mass of the body

g= acceleration of body]

or,     P                                    =  [\d = ; where

v=volume

or,     p                         =         [ \V=A×h  A® Area

h= height ]

or,     p                         = dhg. Proved.

Study the given figure and answer the following questions.

1)      Which tank will experience more pressure at the base. Why?

Ans:  Tank a will experience more pressure at the base. Because, the depth of liquid column is more in tank A than in tank B. We know that the liquid pressure is directly proportional to the depth of liquid column and is independent to the volume of liquid [\P=hdg]

Q.      Study the given figure and answer the following questions.

i) On what surface of the body, the pressure is maximum?

- The pressure is maximum on face CD. Because this face lies at more depth from the free surface. Since liquid pressure µ depth of liquid from the free surface.

ii) What will be the resultant of pressure on AD & BC?

·         The resultant of pressure on AD and BC is zero. As the pressure in these two faces acts equal and in opposite direction.

iii)  What is the effect of pressure difference between two faces AB and CD?

·         The difference in pressure in these two faces generates up thrust.

Study the given figure and answer the following questions.

i) Which device is shown in the figure?

- "Hydraulic press" is shown in the figure.

ii) On which principle is it based? State it

·         It is based on Pascal's law which states that "the external pressure applied on a liquid contained in a closed vessel is transmitted equally and perpendicularly in all the directions"

iii) What is the use of this device?

·         This device is used to lift the heavy equipments (load) by applying small force.

iv) What is the role of the liquid in the given figure?

·         The role of the liquid in the hydraulic press is to transmit the pressure from small piston to the large piston.

v) Why the force applied on the small piston?

- Since pressure is inversely proportional to the area. Hence, the applied force generates high pressure on small piston.

Prove that,

U=vdg, where symbols carry their usual meaning

where;

u = upthrust

d = density of liquid

v = volume of liquid displaced

g = acceleration due to gravity

Solution;

Let us consider a cylindrical object is immersed in a liquid of density 'd' contained in a vessel let 'h1' be the depth of the upper end of cylinder from the free surface and 'h2' be the depth of the lower end of the body from free surface of the liquid as shown in the above figure.

Here,

The liquid pressure at upper surface,

P1 = h1.d.g. ...................eqn (i)

[where, g ® acceleration due to gravity'

The Force at upper end;

F1 = P1 × A1 .....................eqn (ii)

[where A1 ®Area of upper surface]

Now,

From eqn (i) and (ii)

F1 = h1 dg A1 .................eqn (iii)

Similarly, Force on lower end,

F2 = h dg A2 .................eqn (iv)

Since, Upthrust (U)     = F2 - F1

= h2dg A2 - h1 dg A

= dg (h2A2 - h1 A1)

Since the object is symmetrical, A1 = A2

U         = dg (h2 A - h1 A)

= dgA (h2 - h1)

But,

h2 - h1 = h; which is the height of the object.

or,        U = vdg           [where v =  A × h is the volume of substance]

Q.      Write any three properties of liquid pressure?

i)  The pressure given in liquid is distributed equally in all the directions.

ii) A liquid maintain its own level.

iii) The pressure of liquid is independent of the shape of the container in which it is kept .

Q.      The weight of the stone is measured in three different media A,B and C study the given table and answer the following questions.

 Medium Weight A 20 N B 12 N C 16 N

i)       Which one is air, water and salt solution among A,B and c Why?

- From the table.

Medium A ¾¾® Air

Medium B ¾¾® Salt solution

Medium C ¾¾® Water

Out of the given medium air, water and alt solution the density of air is minimum and it exerts minimum upthrust. As a result, weight of a body should be minimum in the air. In the given table weight of a body is maximum in medium A Hence, "A" must be the air.

Again the upthrust exerted by the salt solution is maximum and the weight of a body should be minimum in the salt solution. In the given table, weight of the body is minimum in medium B. Hence "B" must be the salt solution.

And the rest medium i.e. "C" is the water

ii) What will be water displaced?

Solution,

Weight in air (w1) = 20 N

Weight in water (w2) 16 N

Now,

We know,

Upthrust          = w1- w2

= 20 N - 16 N

= 4 N

= weight of water displace.

Q.      What is  error in given figure regarding the level of liquid. Why?

- The level of liquid in column B is less than in column A and column C. Which is the error in the given figure. Because liquid maintains its own level.

Q.     What are fluids?

- Any thing that can flow or blow are called fluids.

Q.      The upthrust of the stone is measured in three different media; A, B and C. study the given table and answer the following question.

 Medium Upthrust A 40 N B 60 N C 30 N

i)       Which one is air water and salt solution among the given media? Why?

- From the table

Medium           B         = Salt solution

Medium           C         = Air

Medium           A         = water

Out of the given medium Air, water and retribution, the upthrust exerted by salt solution is Maximum. Hence according to the table B is salt solution. The upthrust exerted by air is minimum. Hence C is air and the remaining A is water in the given table.

Practice  Question

Q)     What is hydraulic garage lift ? On which principle it is bared? State the principle.

Q)     Why doesn't the pressure of atmosphere break windows?

Q)     Why does a man weigh lighter in air than in vacuum?

Q)     It is easier to pull a bucket from well until it is a water. Why?

Q)     Why a balloon filled with hydrogen?

Q)     Can a substance heavier than water float in it? How?

Q)     Will a hydrogen filled balloon raise in moon? Why?

Q)     The ships can carry more cargo in sea water than in river water. Why?

Q)     Wooden sleepers are used below the rails Why?

Q)     What is the cause of upthrust?

Ans:  When a substance is partially or wholly immersed in a liquid the upper and lower surfaces feel different pressures. This difference in pressure causes a resultant upward force which is  called upthrust.

P2 >  P1; as h2 > h1

Q)     Why are passengers advised to remove ink from their pens while going up in the aeroplane?

Ans:  The atmospheric pressure goes on decreasing with increase in altitude. So, the ink level which was previously at a compressed state will rise up. This may cause overflow of the inks. So, in order to avoid it, passengers are advised to empty the ink before lying.

Q)     What is the apparent weight of a floating body? Explain

Ans:  The apparent weight of a floating body is zero Newton.

Since, W apparent = W true - upthrust

For a floating body W true = upthrust

\ W apparent   =  O  Thee force body will be weightless.

Q)     An iron ball sinks in water but floats in mercury. Why?

Ans:  Iron is highly dense compared to water. When an iron ball is placed in water it can displace very less weight of water. So, it sinks in water. But iron is less dense compared to mercury. When placed in mercury the weight of mercury displaced will be very high and will exceed the weight of iron ball. So iron will flat on mercury.

Q)     A fish can raise and descend in water. how?

Ans:  According to law of floatation, A body floats in liquid if it can displace the liquid to its weight. When a fish stores more air in it, it can cover more volume and can displace more water than its own weight and raises u. But when it releases air the displaced wt. of water will less than the weight of fish themselves and starts to sink.

Q)     A body is thrown into a deep pond. As it sinks deeper and deeper into water does the upthrust (buoyant force) increase or decrease?

Ans:  Since, upthrust (U) = Ndg

v® vol. of liq. displaced

d ® density ; g ® acceleration due to gravity.

Whether a body sinks less or more, the volume of liquid displaced the density and the acceleration due to gravity are same. Hence, upthrust exerted on body is same.

Pressure Numerical

Q)     A sold object weighs 24N in air and 10 N in water what is the upthrust of the liquid on the object? What is the upthrust and weight of the liquid displaced?

Q)     If pistons A, B and C of the apparatus

given in the diagram are supposed to

be frictionless, what i the area of

piton B? What force is

exerted in piston C? [Ans: ]

Q)     What is the volume of water

displaced when a wooden box

of length 50cm, breadth 40 cm

and thickness 30 cm is immersed in

water? [density of water

= 1 gm/cm3 and density of wooden box= 0.56 gm/cm3

1)      A model weighing 54 kg wears high heels with surface area 20 cm2 each. Calculate the pressure exerted by her on the ground.

Sol,

Weight of model (w)     = mg

= 54×10

= 540 N

Surface area of a heel (a)           = 20 cm2

= 20×cm×cm

= 20× m × m

= 2×10-3 m2

\Total surface area (A) = 2×2×10-3 m2

Pressure exerted (p) = ?

we know that,

P =

=

= 135000N

\The girl exerts the pressure of 135000 N.

2)      Calculate the pressure at the bottom of the tank of height 1m 75% of which is filled with the liquid of density 100 kg/m2

Sol,

Height of tank (H) = 1 m

Now,

depth of liquid  column from free surface is;

h = 75% of h

= ×1 = 0.75 m.

density of fluid (S) = 1000 kg/m3

acceleration due to gravity (g) = 10m/s2

Pressure (P) = ?

we have

P = sgh

= 1000×10×0.75

= 7500 Pa.

\Pressure at the bottom = 7500 Pa.

3)      If cross sectional area of piston a

A is 20 cm2 and effort of 50 N is

applied on A, how much load is needed

on pistonB to balance it?

Sol,

For Piston A                                     For Piston B

Area (A1) = 20 cm2 =2×10-3m2      Area (A2) = 60cm2 = 6×10-3m2

Force (F1) = 50 N                          Force (F2) = ?

Let pressure at A be P1 and that in B be P2.

Since pressure is equal at both pistons.

P1=P2

=

or      = =

F2 = 25×6 = 150N

\A load of 150 N is req. to balance the piston.

4)      Calculate the mass of water displaced when a piece of ice having 40 cm length, 20 cm breadth and 15 cm height is kept or water. The density of ice and water is 0.92 gm/cm3 and 1 gm/cm3 respectively.

Sol,   (v1)

Volume of ice     = l×b×h

=40×20×15

= 12000 cm3

density of ice (S1) = 0.92 gm/cm3

density of water (S2) = 1 gm/cm3

volume of water displaced (v2) = ? let m1, and m2 be masses of ice

and water respectively

Acc. to law of floatation,

Weight of ice =  weight of water displaced

or,     M1 × S1 = M2

= 12000×0.92

= 11040 gm

\Mass of water displaced = 11040 gm,

5)      Study the given figure and answer the

questions.

i) Which principle is explained by

the given figure.

- It explains the Archimedes's principle.

ii) What is the upthrust acting on the body. Why?

- Teh upthrust acting on the body is 2 N. Because according to Archimedes uptrhust = wt. of liquid displaced.

iii) What will be the wt. of object in air here

wt of object in water = 10 N

wt of liquid displaced = 2 N

liquid upthrust = 2 N

Hence, wt in air = 10N+2N=12N

iv) Calculate the mass of body in air

Since,     w = mg

or         12 = M×10 = m=12 kg

[Mass is measured  in air]

6)      An ice block (60cm×40cm×30cm) is floating on water. What portion of ice should be outside the water is the density of ice is 0.75 gm/cm3

Sol,

Given

Volume of ice block      = (60×40×30)cm3

= 72000 cm3

density of ice (S1)          = 0.75 gm/cm3

density of water (S2)     = 1 gm/cm3

vol. of water displaced (v2) = ?

Acc. to law of floatation,

wt. of ice = wt. of water displaced

or,     mice × y = m water ×y

or,     v1×s1 = v2 ×s2

or,     = v2

r2 = 54000 cm3

Since, vol. of water displaced is equal to vol. g ice inside water, vol. of ice outside water,

= (72000 - 54000) cm3

= 18000 cm3

\ Portion of ice above water    =

=  past.

7)      The ratio of areas of piston A and B shown in the following diagram is 1:20. Find the load that can be lifted at the piston B by applying 100 N effort at the piston A.

Sol,

Let A1 and A2 be the cross

sectional areas of the piston

A and B respectively.

Given,

=

Effort applied at piston A (F1) =  100N

Load lifted at piston B (F2) = ?

Using Pascal's  law,

=

or,      =

\ F2 = 1000 N

\ 1000 N load can be lifted at piston B by applying 100 N force at piston A.

8)      Find the pressure exerted by the following box. The density of the box is 3000 kg/m2 and g=9.8m/s2

Given,

Density (S)        = 3000 kg/m2

Volume (V)       = 2m×1.5m×2m

= 6m3

Area of the bottom (A) = 2 m×1.5m = 3m2

we have,

Mass (M)           = Vol. ×density

= 6×300 kg

Again,

Force (F)            = mg

= 18000×9.8

= 176400 N

Now,

Pressure (P)        =  =

Thus, the pressure exerted by the body is 326.67 Pa.

9)      The area of the edge of a knife is 0.3cm2. 75 N force is applied on the head of knife find the pressure exerted by the knife on the material to be cut.

Given,

Force (F)            = 75N

Area (A) = 0.025 cm2 = 0.03 m2 = 0.00003 m2

1000×100

Now,

Pressure (P) =   =  Pa = 2.5×100 Pa.

Thus, pressure exerted by the knife is 2.5×107 Pa.

Pressure

Practice Questions.

Q)     A cube of side 0.5 m and density 8000 kg/m3 is placed on a table. Find the pressure exerted by the cube on the table. [g=9.8m/s2]                                              (Ans. 19600 Pa)

Q)     A man exert 32666 Pa pressure on the ground. If his feet occupy the area of 150 cm2 find the mass of the man if g=9.8m/s2 (Ans: 49.99 kg.)

Q)     A boat of mass 200 kg displaces maximum of 3m3 water when it is floating. Find the maximum mass of load the boat can carry safety. the density of water is 1000 kg/m3

(Ans: 2800 kg)

Q)     What will be the pressure exerted at a depth of 6m in a pond where the acceleration due to gravity is 9.8m/s2 (Density of water = 1000 kg/m3)

Q)     The weight of an object is 20N in air, the weight of that object in the water is seen 12 N only then;

i) What is the value of upthrust on the body?

ii) What is the weight of the displaced water by it?

Q)     There are 2 pistons A and B. The area of A is 100cm2 and that of B is 0.9 m2. If the force of 101.3N is applied at piston A calculate the force at piston B.

Pressure

Solution (Numerical)

Q)     A block of wood floats on a liquid with four-fifth of its volume submerged. If the density of the wood is 800 kg/m3 find the density of the liquid.

Sol,

Let V be the total volume of the block and let 4/5 V be the volume under the liquid.

\ Vol. of liquid displaced = 4/5 V

Here,

Fraction of block inside the liquid (v2/v2) = 4/5

Density of wood (S1) = 800 kg/m3

Density of liquid (S2) = ?

Acc. to law of floatation,

wt of block = wt. of liquid displaced

m1 g       = m2 g

or,     V1 ×S1    = V2 × S2

or,             =

\ S2 =  1000 kg/m3

\ Density of liquid = 1000 kg/m3.

Q)     A balloon filled with air can withstand with maximum of 6.174×105 Pa. Pressure. At what depth of water of density 1000 kg/m3 should it be taken so that the balloon just burst? g= 9.8 m2

Sol,

Given,

Max. pressure (Pmax) = 6.174×105 Pa

Max. depth (Hmax) = ?

Density of water (d) = 1000 kg/ m3

We know that,

P = dgh

or,     6.174×105 = 1000×9.8×h

\ h        =

= 63m

\ It can be taken to maximum depth of 63 m where it just brusts.

Q)     The density of a brick is 2.5 gm/cc and its mass 1 kg. Find the upthrust of water on the brick the density of water is 1 gm/cc.

Given,

Density of brick (d1) = 2.5 gm/cc = 2500 kg/ m3

Density of water (d2) = 1 gm/cc = 1000 kg/m3

Mass of brick (m) = 1 kg

Upthrust (u) = ?

Now,

Volume of the brick (v) =  =   m3 = 0.004 m3

Since,

density of brick is more than the density of water it sinks in water.

for sinking case,

U         = vdg

= 0.0004×1000×9.8

= 3.92 N

\ Upthrust of water on the brick  =  3.92 N.

Q)     Egg sinks in pure water but floats in salty

water why?

- The density of salty water is more

than that of fresh water. As a result

it provides more upthrust to the egg

and hence, egg floats in salty water but

sins in fresh water.

Pressure: Theory practice

Q)     In the given diagram three taps A,B and

C having holes of the same diameter are

connected in tank full of water. In which

tap does more water flow per second and

why?

Q)     It is difficult to immerse empty plastic bottle into water. Why?

Q)     What will be the atmospheric pressure inside vacuum?

Q)     A beiger can sleep on the bed of nails. Why?

Q)     What will happen is the base of a dam is made narrower than the tap?

Q)     Why does a ship carry more load than an aeroplane?

Q)     A stone tied with a string is completely immersed in a liquid. Draw a diagram to illustrate the forces acting on the stone.