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PHYSICS(PART – 1)

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( 4 )

PREFACE

Malcolm Forbes said “Education's purpose is to replace an empty mind with an open one”

and this is something which is always followed by Government of Kerala, Department of Education,

whether through their education system framework or recent enhancement in their curriculum. The

aim of their Curriculum is not just to let learners obtain basic knowledge but to make them life-

long learners.

The purpose of this book is to nurture individuality and thus enhance one's innate potentials

which help in increasing the self-study mode for students. This book strengthens knowledge and

attitude related to subject. This book is designed in such a way that students can set their own goals

and can improve their problem solving and thinking skills.

This book is strictly as per the latest SCERT Kerala Textbook, introduced by SSLC Board in

2016. It follows the latest syllabus prescribed by the board. It contains all types of questions like

Textbook Questions, VSA Questions (Very Short Answer), SA Questions (Short Answer), MCQs

(Multiple Choice Questions) and LA Questions (Long Answer). A synopsis is given for every chapter

which contains important points from that chapter. Each chapter has high quality figures wherever

required for better, fast and clear understanding.

OSWAAL SSLC Question Bank is different and better in terms of High Quality Questions

which are developed by 'OSWAAL Expert Panel' which ensures success in examination. The Question

Bank is arranged ‘Topic-Wise’ where each topic from every chapter is explained in detail. High quality

figures and Flow charts are given to improve retention of concepts.

Through OSWAAL Books students are taught how to think, not what to think. We at

OSWAAL Books try to use quality content, standard language, creativity and high quality figures,

which makes readers to enjoy it because we believe if our readers don't enjoy reading our book then

there is no use in reading it at all. This is one of the reasons that the scope of this book extends from

students to teachers. Teachers can use this book as a perfect teaching guide and students can use

this book for good learning and practice.

At last we would like to thank our authors, editors, reviewers and specially students whom

we request to send suggestions regularly which will help in continuous improvement of this book

and will make this book “One of the Best”. Wish you all Happy Learning.

Why Topic Wise Question Banks are a Better Choice than Previous Year’s Papers ?

Question Banks Previous Years’ Papers

1. Chapter-wise and Topic –wise presentation

in Question Banks facilitates systematic

study.

2. Question Banks can be referred to by the

students throughout the year as well as at

the completion of each chapter in school.

3. Question Banks, take into account any

changes in syllabus or layout and hence are

fully updated and aligned as per the latest

specifications by the Board.

1. Year Wise presentation restricts

methodical flow of learning.

2. These can be referred to only after the

completion of the full syllabus in school.

3. Previous Years' questions cannot be

changed and hence fail to be adept with

the latest Board specifications

–Publisher

CHAPTER

1 FORCES OF FLUIDS

FLOWCHART

QUICK REVIEW

All objects experience a force of buoyancy when they are immersed in a fluid. Weight : Force by which an object is attracted towards the earth. Its SI unit is newton (N). Upthrust / buoyant force : The upward force exerted by a liquid on the body which is immersed in the liquid. Density : It is the mass of a substance per unit volume. Its unit is kilogram per meter cube (kg.m–3). Relative density : It is the ratio of the density of a substance to that of water. It is also called specific gravity. Pressure : Force per unit area. SI unit is N/m2 or N m–2 or Pascal. Objects having density less than that of the liquid in which they are immersed, floats on the surface of

the liquid. If the density of the object is more than the density of the liquid in which it is immersed then it sinks in the liquid.

Archimedes principle : When a body is immersed partially or completely in a fluid (or liquid), it experiences an upthrust that is equal to the weight of the fluid displaced by the body.

Lactometers are used to determine the purity of a sample of milk. Hydrometers are used for determining the density of liquids. Density of different substances are different. Pascal’s Law : It states that if gravity effect is neglected, the pressure at every point of liquid in equilibrium

of rest is same. Pascal’s law also states that the increase in pressure at one point of the enclosed liquid in equilibrium of rest is transmitted equally to all other points of liquid.

TOPIC - 1

TOPIC - 2

TOPIC - 1

TOPIC - 2

6 ] Oswaal Kerala SSLC Question Bank PHYSICS, Class-IX

Laws of floatation : It states that a body will float in a liquid if weight of the liquid displaced by the immersed part of the body is equal to the weight of the body.

(i) When true weight of the body W > w (weight of the liquid displaced), the body will sink to the bottom of the liquid. It will be so when the density of solid body (ρ) is greater than the density of liquid (σ), i.e., ρ > σ.

(ii) When W < w, the body will rise above the surface of liquid to such an extent that the weight of the liquid displaced by immersed part of the body (i.e. upward thrust) becomes equal to the weight of the body. The body then will float. In this case the density of solid body is less than the density of liquid, i.e., ρ < σ.

(iii) When W = w, the body is at rest anywhere in the liquid. The body will float if its whole volume is just immersed in the liquid in this case the density of body is equal to density of liquid, i.e., ρ = σ.

There will be equilibrium of floating body when (a) Weight of liquid displaced by the immersed part of body is equal to the weight of the body.

(b) The centre of gravity of the body and the centre of buoyancy lie along the same vertical line. (c) The centre of gravity of the body lies vertically below the meta centre. The body will be in unstable

equilibrium if centre of gravity lies vertically above the meta centre. Adhesive force : Is the force of attraction acting between molecules of two different materials. For example, the

force acting between the molecules of water and glass. Cohesive force : Is the force of attraction acting between molecules of the same material. For example, the force

acting between the adjacent molecules of water. Caplillary tube : Is a tube with a fine and uniform bore throughout its length. Caplillarity : Is the phenomenon of rise or fall of liquid in a capillary tube. Viscosity : Is the property of liquid due to which a backward dragging force called viscous force act tangentially

on the layer of the liquid in motion.

KNOW THE FORMULAE

1. Density =Mass

Volume

2.

Relative density =

Density of a substance

Density of water

3. Pressure =ThrustArea

MULTIPLE CHOICE QUESTIONS (1 mark each)

Q. 1. When a body is immersed in a liquid, the unit of measuring upthrust acting on it due to displaced liquid is :

(a) Watt (b) Joule (c) Newton (d) Kg m/s Ans. (c) Q. 2. In order to find out the loss of weight in a liquid,

the student has to immerse the body : (a) Partly (b) Completely

(c) In salted water only (d) 14

th of its volume Ans. (b) Q. 3. A body floats in a liquid : (a) When the weight of the body is exactly half of

the weight of the liquid displaced. (b) When the weight of the body is greater than

the weight of the liquid displaced. (c) When the weight of the body is equal to the

weight of the liquid displaced (d) When weight of the body is less than the

weight of the liquid displaced. Ans. (c)

Q. 4. If da and db are densities of the material of body and the liquid respectively, the body can float only :

(a) da = db (b) da < db (c) da > db (d) da = 2db Ans. (b) Q. 5. Upthrust depends upon : (a) Volume of liquid displaced (b) Density of liquid (c) ‘g’ (d) All of these Ans. (d) Q. 6. A jet plane flies in air because : (a) Streamlined flow of air causing lift (b) Upward thrust of air balance its weight (c) No gravity acts on plane (d) None of these Ans. (a) Q. 7. Which of the following has the highest density? (a) Alcohol (b) Glycerine (c) Water (d) Sea water Ans. (b)

FORCES OF FLUIDS [ 7

Q. 8. The weight of a body felt in tap water and salted water are WA and WB respectively then :

(a) WA = WB (b) WA > WB (c) WA < WB (d) WB = WA Ans. (b) Q. 9. Student A wears wide base shoes and student B

wears narrow base shoes while walking on the ice. Who will be able to walk easily and comfortably if both the students have equal weight?

(a) Neither student A nor B (b) Only student B (c) Only student A (d) Both student A and B Ans. (c) Q. 10. When a solid is fully immersed in a liquid, the

volume of the liquid displaced is : (a) Greater than the volume of the solid body (b) Lesser than the volume of the solid body (c) Equal to the volume of the solid body (d) Depends on the way in which solid is

immersed in the liquid Ans. (c) Q. 11. Density of water is maximum at : (a) 0˚C (b) 100˚C (c) 10˚C (d) 4˚C Ans. (d) Q. 12. The buoyant forces applied by the fluid : (a) Increases on increasing the density of the fluid : (b) Decreases on increasing the density of the fluid. (c) Increases on decreasing the density of the fluid.

(d) All of the above Ans. (a) Q. 13. When the angle of contact between a solid and a

liquid is 90˚, then : (a) Cohesive force > Adhesive force (b) Cohesive force < Adhesive force (c) Cohesive force = Adhesive force (d) Cohesive force >> Adhesive force Ans. (c) Q. 14. Which of the following is not based on the

principle of capillarity : (a) Floating of wood on water surface (b) Ploughing of soil (c) Rise of oil in wick of lantern (d) Soaking of ink by bloating paper Ans. (a) Q. 15. The rise of a liquid in a capillary tube does not

depend upon : (a) Angle of contact (b) Density of the liquid (c) Radius of the capillary tube (d) Atmospheric pressure Ans. (d) Q. 16. For a liquid, which is rising in a capillary tube,

the angle of contact is : (a) 90˚ (b) 180˚ (c) Acute (d) Obtuse Ans. (c)

Very Short Answer Type Questions (1 mark each)

Q. 1. A body which floats on water sank, when put in an kerosene. Why did it happen? [T.B.Q.]

Ans. When density of body is less than the density of water and more than the density of oil, the body will float in water and sink in oil.

i.e. dwater > dbody > doil 1 Q. 2. Give reason, why a block of plastic when released

under water comes up to the surface of water. Ans. Density of a plastic block is less than the density

of water, and hence, the upthrust buoyant force of water on plastic block is more and it comes up to the water surface. 1

Q. 3. When we jump into a swimming pool, we feel lighter. Why ?

Ans. This happens because upthrust acts on us and our apparent weight becomes less than actual weight.

Apparent weight = Actual weight – Upthrust. 1 Q. 4. What is the formula for relative density ?

Ans. Relative density = Densityof thesubstanceDensityof water 1

Q. 5. What are fluids ? Ans. A substance that can flow is called a fluid. Hence

liquids and gasses are collectively called fluids. 1

Q. 6. Why does a mug full of water feel lighter inside the water?

Ans. Because of upthrust of water exerted on the mug, its apparent weight becomes less than its actual weight. 1

Q. 7. In what direction does the buoyant force on an object immersed in a liquid act?

Ans. Buoyant force on an object immersed in a liquid acts in the vertically upward direction. 1

Q. 8. Two blocks, one of iron and other of wood, are immersed in the water at the same depth. Which will come up and why?

Ans. Wooden block will come up because density of wood is less than the density of water and hence upthrust acting on wooden block wil be more than its actual wieght. 1

Q. 9. Why does a cork released under water come up to the surface of water? Explain

Ans. The density of cork is less than that of water. It means its weight is less than the buoyant force experienced by it under water. So on releasing it comes to the surface of water. 1

Q. 10. Define capillarity Ans. Caplillarity is the phenomenon of rise or fall

of liquid in a capillary tube due to difference in adhessive and cohessive forces. 1

Q. 11. What will happen if the length of the capillary tube smaller than the height to which the liquid rises?

8 ] Oswaal Kerala SSLC Question Bank PHYSICS, Class-IX

Ans. The liquid will not over flow in the capillary. It will be full upto the top of the capillary. 1

Q. 12. Ridhaan places a piece of iron on the surface of water. What will happen? Give reason.

Ans. The piece of iron will sink in the water as its density is more than the density of water. 1

Q. 13. Where and why high viscosity liquids are used in trains?

Ans. High viscosity liquids are used as buffers in trains so that the shocks may be absorbed easily. 1

Short Answer Type Questions - I (2 marks each)

Q. 1. The weight of a piece of stone in air is 120 N and its weight in water is 100 N. Calculate the buoyancy, experienced by the stone. [T.B.Q.]

Ans. We can see in the diagram that Buoyancy=120−100 Buoyancy = 20 N

100 N

120 N

Buoyancy

2 Q. 2. Which is the correct figure? Why? [T.B.Q.]

Fig. A Fig. B

Ans. Figure A is correct because, the meniscus is convex and in that case level of fluid falls as the intermolecular forces within the liquid exceed those between the solid and the liquid. 2

Q. 3. Write down the reason for the following : (a) Ink can be blotted with chalk. (b) Sweat can be blotted with tissue paper. [T.B.Q.] Ans. (a) Chalk has fine pores which act as capillaries.

The ink rises in these capillaries. 1 (b) Tissue paper has fine pores which act as capillaries.

The sweat rises in these capillaries. 1 Q. 4. A boy gets into a floating boat : (a) What happens to the weight of water displaced ? (b) What happens to the buoyant force ? Ans. (a) The weight of the water displaced is increased

because the weight of the boat is increased. Weight of water displaced will be equal to the buoyant force which is equal to the weight of the boat and boy.

(b) The upthrust increases because when an object floats in water then

Buoyant force = Weight of fluid displaced by object. 2 Q. 5. A woman walking on a wooden floor wearing

high-heels can damage the floor by making small dimples in the floor since her weight is concentrated on such a small area (the tip of the high heal). If the woman weighs 600 N and the tip of the high heel is 1 cm2, what will be the pressure exerted on the floor by her high heels ?

Ans. Thrust F = 600 N, Area A = 1 cm2 = 1 × 10−4 m2 ½ Pressure = F/A ½ = 6 ×106 Pa. 1 Q. 6. Anil argues with Sunil. According to Anil, we

weigh less in water than in air, but Sunil opposes it. Who is correct-Anil or Sunil? Which is the principle used by the correct one ?

Ans. Anil is correct. His argument is based on the Archimedes

principle which states that when a body is partially or completely immersed is a liquid at rest, it experiences upthrust equal to the weight of liquid displaced. 1+1

Q. 7. The volume of 50 gm of a substance is 20 cm3. If the density of water is 1 gm cm-3, will the substance float or sink in water? Justify your answer.

Ans. Volume of substance = 20 cm3, mass of substance = 50 gm. ½

∴ Density of substance, = 5020

= 2.5gm / cm

Density of water,

3d

d

s

w =1gm / cm

It willsink.

3

d dw s<∴

½

Q. 8. (a) State the principle on which the working of a hydrometer is based.

1

(b) A sharp knife is more effective than a blunt knife. Why?

Ans. (a) It is based on the Archimedes principle, greater the density of liquid in which a body is immersed, lesser is the volume submerged.

(b) Sharp knife has less surface area than blunt knife. The pressure is inversely proportional to area hence, it exerts more pressure. 1+1

Q. 9. (i) Define relative density of a substance. (ii) The density of iron is 7.8 × 103 kg/m3 and that

of water is 103 kg/m3. Find the relative density of iron.

FORCES OF FLUIDS [ 9

Ans. (i) Relative density of a substance is the ratio of the density of the substance to the density of water.

Relative density = Densityof thesubstanceDensityof water

(ii) (ii) Relative density of iron = = 7.87.8 10

10

3

3

×. 1+1

Q. 10. When an object is immersed into the fluid, two forces act on the object in the vertically opposite directions. Name these forces and also write the factors on which the magnitude of these forces depends on.

Ans. Name of the forces : (i) weight of the object, (ii) Upthrust. ½+ ½

Magnitude of weight depends on : (i) Mass of the object. (ii) Acceleration due to gravity.

Magnitude of Upthrust depends on : (i) Volume of object immersed. (ii) Density of the fluid. (ii) Acceleration due to gravity. ½+ ½

Q. 11. The density of turpentine at 293 K is given as 870 kg/m3. Identify and write the name of substances that sink in turpentine at the same temperature.

S. No. Substance Density kg/m3

1.2.3.4.5.6.

WoodIce

RubbeParaffin wax

CorkBone

6909209709002401850

Ans. The substances that sink in turpentine oil are ice, rubber, paraffin wax and bone. ½ × 4 = 2

Q. 12. Define buoyant force. An object of volume 5 cc is immersed first in water and then in salt solution. In which case will it experience a greater buoyant force? What will be the effect on the buoyant force if the volume of the object is increased to 8cc?

Ans. An upward force exerted on an object when immersed in a liquid is called buoyant force.

The object will experience greater buoyant force in the salt solution. Since the density of salt solution is more than density of water. If the volume of object is increased then the buoyant force will also increase. 1+½ + ½

Q. 13. (a) An object of volume V is immersed in a liquid of density ρ. Calculate the magnitude of the buoyant force acting on the object due to the liquid.

(b) Mention the direction of the buoyant force. Ans. (a) Volume of the immersed body = Volume of the

liquid displaced ½ Mass of the liquid displaced = Vρ ½ Weight of the liquid displaced = Buoyant force

= Vρg ½ (b) Buoyant force acts in vertically upward direction.

½ Q. 14. An object is suspended with a string and the string

gets stretched. When the object is completely immersed in water, the extension of thread decreases. Explain why it so happens.

Ans. This is because of the buoyancy as the net tension acting on the string gets reduced and as a result lesser downward force is experienced. 1

The net force on the string = Gravitational pull – Buoyancy Buoyancy acts in a direction opposite to the

gravitational pull (weight). 1 Q. 15. Out of the two positions given below, in which

case do you apply more pressure on loose sand and why?

(i) While you are standing. (ii) When you lie down. Ans. (i) More pressure is applied while standing

because area of contact is less and pressure is inversely proportional to area of contact. 1+1

Q. 16. Give reason for the following: (i) Cutting and piercing tools are made sharp. (ii) An egg sinks in fresh water, but floats in highly

salty water. Ans. (i) Sharp edges will reduce the area and hence,

more pressure can be applied with the same force. (ii) Density of an egg is more than the density of

fresh-water, but less than the density of highly salty water. 1+1

Q. 17. What happens when : (a) Buoyant force exerted by the fluid is greater than

the weight of the body. (b) Buoyant force exerted by the fluid is equal to the

weight of the body. Ans. (a) Body will move up to the surface and float. (b) Body will float, but will remain suspended in the

fluid. 1+1 Q. 18. A balloon filled with hydrogen gas floats in the

air. Explain this fact with reason. Ans. The density of hydrogen is less than that of

air, i.e., hydrogen gas is lighter than air and the upthrust acting on the balloon is equal to the weight of the balloon. Hence, it makes the balloon to float in air. 2

Q. 19. State the conditions under which a body will either sink or float on the surface of water. Explain each condition too.

Ans. If the density of body is less than that of water, the upward thrust of buoyancy due to displaced water will be equal to the weight of the body; so it will float. If the density of object is more than that of water, the upward thrust will be smaller than the weight of the body; so it will sink. 1+1

Q. 20. The pressure exerted by the weight of a cubical block of side 4 cm on the surface is 10 pascal. Calculate the weight of the block.

Ans. Area = (0.04)2 m2 = 0.0016 m2

P =A

10 =0.0016

= 0.0016 10

mg

mg

mg ×

=1.6×10–2 N. 1+1

Oswaal Kerala SSLC Question Bank ForClass 9 Physics (Part-1) With Complete

Solutions For 2017 Exam

Publisher : Oswaal Books ISBN : : 97893861775 Author : Panel Of Experts

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