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# Solutions of CBSE Class 9 Science Question Paper 2020

The solutions of CBSE class 9 science question paper 2020 is beneficial for the students of CBSE 9 class. Study of solutions of class 9 science question paper 2020 will provide you an idea about the type of questions asked in the exams. Solutions of 2020 science question paper of 9 class CBSE  will give you complete information regarding the latest syllabus of science. All questions of the 2020 science question paper are solved by an expert on the subject as per the CBSE norms. The study of last year’s question paper’s solutions is the precious study material for getting excellent marks in the exams, the study of these solutions boosts the confidence of students, these solutions equip the student, with determination, enthusiasm and willpower in achieving their target.

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CBSE Class 9-Unsolved question paper of science 2019

SECTION –A                                                            20 ×1=20

Q1. Underline what conditions will the magnitude of displacement be equal to the distance travelled by an object?

Ans. When an object moves in a straight line or say the object is following a linear motion in a particular direction then the total distance travelled by the object is equal to the displacement.

Q2.Write down the equation for velocity-time relation.

Ans. v = u + at, where v= final velocity of the object in motion. u = Initial velocity of the object in motion

a = acceleration of the object. t = time taken by the object in changing the velocity from u to v.

Q3.Name the process used by milkman to separate cream from milk.

Ans. Centrifugation

Note- Centrifugation is the process when a rotter is installed in a closed container and it is allowed to rotate, the liquids around it also rotates at the speed of the rotor, an outward force is exerted on the particles available in the liquid. Heavy particles go farther in comparison to light particles, such a process which is used for separating the particles in a mixture is known as centrifugation.

Q4.Name the element with atomic number 12.

Ans. Magnesium-Mg

Note- Remember the whole table of elements and their atomic numbers mentioned in NCERT chapter-4

Q5.Name the air-borne disease.

Ans. Coronavirus

Q6.Name the cell organelle which has its own DNA and ribosomes.

Ans. Both mitochondria and chloroplasts contain their own DNA and ribosomes.

Q7.When ice melts, the cooling is produced because:

a) density of ice is less than water.

b) Ice floats on water.

c) melting point of ice is 0⁰C.

d) Ice absorbs heat from the surroundings.

Ans. Ice absorbs heat from the surroundings.

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Q8.When stained appropriately the muscle which shows alternate light and dark bands is:

a) Striated       b) Smooth      c) Cardiac      d) Unstriated

Ans. Striated muscle

Q9. A student took some dilute sulphuric acid in a conical flask and added some pieces of metal into it. He observed bubbles of colourless and odourless gas. This gas is:

a) Oxygen    b) Hydrogen sulphide    c) Hydrogen    d) Sulphur dioxide

Ans. Hydrogen gas

Note – Metal + acid → Salt + Hydrogen gas

Q10.A man is standing on a boat in still water. If he walks towards the shore, the boat will:

a) Move away from the shore                                             b) move towards the shore

c) Remain stationary                                                            d) Sink

Ans. A man standing in a boat in still water. if he walks towards the shore the boat will move backwards because of the third law of motion.

Note- Man applies a force in the forward direction to move towards the shore, according to newton’s third law equal amount of force exerted by the man to the boat that moves boat in the backward direction.

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Q11.Sachin was asked to separate a mixture of common salt and ammonium chloride. Identify the process used by Sachin:

a) Sedimentation                                      b) Sublimation

c) Distillation                                             d) Crystallization

Ans. Sublimation

Note-Sublimation is the process in which a solid change directly to gaseous state or gas directly changes to solid.

Q12.Carbohydrates are stored in plants in the form of :

a) Sucrose                                                b) Starch

c) Glycogen                                              d) Crystallization

Ans. Starch

Note- Starch is one of the types of carbohydrate which is a complex carbohydrate while sugar is known as a simple carbohydrate.

Q13.Sound will not travel through:

a) Solid                                                       c)Liquid

b) Gas                                                        d)Vacuum

Ans. Vacuum

Note- Sound is needed medium, solid, liquid or gas to travel

Q14.The acceleration of a car that speeds up from 12 m/s to 30 m/s in 15s is:

a)4 m/s2                                                     c)1.2 m/s2

b) 2 m/s2                                                    d) 5 m/s2

Ans. 1.2 m/s2

Note- Acceleration = Change in speed/time = (30 – 12)/15 = 18/15 = 6/5 =1.2 m/s²

Q15.Tyndall effect can be observed easily in which type of solutions.

a) True solution

b)Colloidal solution

c) Suspension

d)Both (b) and (c)

Ans.d)Both (b) and (c)

Note – The particle size of the dispersed phase in a colloid are larger than the size of the solution,  particles size of colloid is enough to scatter the light in all direction and hence shows Tyndall effect since the particle size of suspension is more than the size of colloid so suspension also shows Tyndall effect.

Q16.To which group does Agaricus belong:

a) Algae                                                           c) Fungi

b) Bryophyta                                                  d) Porifera

Ans. Fungi

Q17.Which of the following organelles is not present in the cheek cell?

a) Ribosomes

b) Mitochondria

c) Chloroplast

d) Nucleus

Ans. c) Chloroplast

The cheek cell contains cell organelles like Ribosomes, Mitochondria, Chloroplat and Nucleus while chloroplast is found in plant cell and used in the conduction of the photosynthesis process.

Q18.Which of the following mixture is unstable:

a) Water +Sugar                                           c) Water + Sand

b) Water + Salt                                              d) Water + Copper sulphate

Ans.  c) Water + Sand

Note- Sugar, salt and copper sulphate are completely dissolved in the water, so these are solutions and type of such mixtures are known as a stable mixture while sand is not completely dissolved in water and after some time sand is deposited at the bottom, so it is suspension and such type of mixture is known as an unstable mixture.

ASSERTION and REASON (QNos. .19 & 20)

In questions 19 and 20, a statement of assertion (A) is followed by a statement of the reason

a)A is true but R is false.

b)A and R both are true and R is the correct reason of A.

c)A is false but R is true

d)A and R both are true but R is not the correct reason of A.

e)Both A and R are false.

Q19.Statement-You falls in the forward direction when a moving bus stop suddenly.

Reason-   We fall forward due to inertia of motion of the upper part of the body.

Ans.b)A and R both are true and R is the correct reason of A.

Note- When a moving bus stops suddenly, the lower part of our body also stops because it is attached with seats of the bus but due to inertia upper part of the body remains to continue to move with the speed of bus thereby our head struck to next seat.

Q20. Statement-Metals are electropositive in nature.

Reason- Metals lose electrons in order to become stable and form cations.

Ans.b)A and R both are true and R is the correct reason of A.

Note- Metals has a tendency to donate electrons that makes metals electropositive in nature.

SECTION−B          10 x 3=30

Q21.Position−time information for a cheetah is shown in the data table below. Assume that the motion is uniform, fill a,b in the blanks of the table and calculate the speed of Cheetah.

 Time(S) Position(m) 0 0 0.5 12.5 1.0 (a) 1.5 37.5 2.0 50.0 (b) 62.5

Ans. Let the speed of Cheeta is = v

$\boldsymbol{v =\frac{12.5-0}{0.5-0}=\frac{12.5}{0.5}=25\: m/s}$

$\boldsymbol{\frac{a-0}{1-0}=25}$

a = 25 m/s

$\boldsymbol{\frac{62.5-0}{b-0}=25}$

25b = 62.5

$\boldsymbol{b=\frac{62.5}{25}=2.5}$

Hence a = 2.5 s

Q22.Define law of conservation of momentum, Derive a mathematical expression for the same.

Ans. Law of conservation of momentum states that if a change occurs in a system in an isolated condition then the initial momentum of the system always is equal to the final momentum of the system. As an example, if two objects colloids with each other then their initial momentum is equal to their final momentum.

Let two objects  A and B of the masses m1 and m2  are moving with the velocity u1 and u2

After the collision, their velocity becomes v1  and v2

As we know the momentum = mass × velocity

Sum of initial momentum of both objects  = m1 u1 + m2 u2

Sum of final momentum of both objects = m1 v1 + m2 v2

According to conservation of momentum

The initial momentum of both objects = Final momentum of both objects

m1 u1 + m2 u= m1 v1 + m2 v2

What-is-second-law-of-of-motion?

Q23.a) Define acceleration due to gravity.

b)At the equator, a bag of sugar weighs W kgs. Will it weigh the same. Or more or less? When taken to America? Give the reason for your answer.

Ans.

a) An object moves downward or upward to the earth is under the impact of the gravitational force, when it is thrown upwards its speed slowed down and after reaching to certain height speed becomes zero and then it returns back towards the earth and then its speed increases as it approaches nearer to the earth, it happens because of the acceleration due to gravity, so acceleration due to gravity can be defined as the rate of change of  the velocity of an object due to the gravitational force of the earth , it is a constant quantity and measured 9.81 m/s².

(b) The relationship of gravitational acceleration with the radius of the earth is expressed as follows

$\boldsymbol{g=G\frac{M}{R^{2}}}$

Where G= Universal constant of acceleration, R = Radius of the earth, M= Mass of the earth

The earth is bulged out at the equator and flattened at the poles, the radius of the earth is more at the equator in comparison to poles. America lies at the northern hemisphere so the distance of this location with respect to the centre of the earth is slightly lesser as compared to the equator. As it is seen in the equation that the value of g is less if the radius is more, so the value of g would be slightly more in America as compared to the equator, hence a bag of sugar weighs at America would be slightly more than W kgs.

What-is-universal-law-of-gravitational-force?

Q24.Rahul and Manav each were given a mixture of iron filings and sulphur powder. Rahul heated the mixture strongly and a new substance was formed. Write three points of difference between the two.

Ans.In the case of Rahul (i) Mixture of  Iron filings and sulphur powder when heated forms FeS(iron sulphide) (ii) A homogenous mixture is formed blackish in colour (iii) FeS doesn’t show any reaction in further heating.

In Manav case (i) Iron filings and sulphur retain their original properties.(ii) The mixture of iron and sulphur is heterogenous and separable (iii) The mixture of iron and sulphur powder can be separated through the magnet.

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Q25.Explain the observations of Rutherford’s scattering experiment (diagram also).

Ans. Rutherford bombarded α particles on thin gold foil and got the following observations.

(i) Maximum α particles penetrated through the gold foil indicates that the larger area of the atom is empty.

(ii) Some of the α particles deviated through a certain angle indicate that at the centre positive charge is located occupying a lesser area since positive charge repels another positive charge.

(iii) Very few of the α particles bounced back by 180º angle, indicates that positive charge at the centre occupies very less volume as compared to the whole of the atom.

Q26.An object of mass 100 kg is accelerated uniformly from a velocity of 5 m/s to 8 m/s in 6 seconds. Calculate the initial and final momentum of the object. Also, find the magnitude of the force exerted on the object.

Ans.

Mass of the object, m = 100 kg

Initial velocity, u of the object = 5 m/s

Final velocity, v of the object = 8 m/s

Initial momentum of the object = mu = 100 × 5 = 500 kg-m/s

Final momentum of the object = mv = 100 × 8 = 800 kg-m/s

Time, t = 6 seconds

Force = Rate of change of momentum

Q27.What are the weeds? Write two methods of weed control.

Ans. The unwanted plants that grow in the field and compete with the crop plant for sunlight, space and nutrition and water are called weeds.

The two methods of weed control as follows:

1. Mechanical method – In this method the weeds are cleared by using mechanical tools like a hoe.

2. Biological method -involves the deliberate use of insects or some other organisms which consume and specifically destroy weed plants.

Q28.Sulphur has atomic number 16 and mass number 32. State the number of proton and neutrons present in the nucleus of sulphur. Give a simple diagram to show the arrangement of electrons in an atom of sulphur.

Ans. The atomic number of sulphur = 16

Number of protons in  atom = Atomic number  = 16

The number of protons + Number of neutrons = Mass number

Since the mass number of sulphur atom = 32

∴ Number of neutrons in sulphur atom = 32 – 16 = 16

We know the number of protons in an atom = Number of electrons in an atom

The number of electrons in sulphur atom = 16

Electronic configuration in the sulphur atom is given as follows

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Q29.Explain the direction of movement of air during the day and night in coastal areas.

Ans. In coastal areas, during the daytime, there is a regular flow of cool air from the sea towards the land. At night, there is a reverse flow of air from land to sea. This happens because, during the daytime, the land gets heated faster than water and radiated heat from land, heats the air above it. The hot air rises and creates an area of low pressure.Sea water does not get heated rapidly, so the air above it is cooler than the air above land creating high-pressure area above the sea. The pressure difference between the area above seawater and the air above land area forces the airflow from sea to water. During the night time, the flow of air reverses because seawater takes time to cool, the air above the sea gets heated so the air above seawater creates a low-pressure area. At night the land cools rapidly, the air above land gets cooled that creates high-pressure area above the land. The pressure difference between sea and land forces the airflow from land to air.

Q30.a)Define hybridization. How is it useful for the crop; variety improvement?

Ans. The hybridization is one of the methods of crop variety improvement to increase the yield of crop production. In this method, two dissimilar plants of the same type of crop have crossed that results to produce high-quality seeds with high productivity.

The world population is increasing day by day, the area used for crop production is limited, so the requirement is high with limited resources. Hybridization is the technic used for increasing the yield of crop production, Hybrid seeds are disease resistive and maintain uniformity of seeds.

b). How much would a 70 kg astronaut weight on moon? What would be his mass on the earth and the moon?

Ans. The gravitational acceleration at the moon is one-sixth of earth’s gravitational acceleration. The  70 kg is the mass of astronaut,

$\boldsymbol{g'=\frac{g}{6}}$

Where g is the gravitational acceleration at the moon and g’ is the gravitational acceleration at the moon

The value of g = 9.8 m/s²

The weight of  astronaut at the moon = Mass of astronaut × Gravitational acceleration at the moon

$\boldsymbol{= 70\times \frac{g}{6}=\frac{70\times 9.8}{6}=114\: N}$

The weight of the astronaut at the moon = 114 N

The mass is a constant everywhere in the universe so the mass of the astronaut in the moon and the earth will be 70 kg.

SECTION−C                                                                       6 × 5 =30

Q32.An atom of an element’ ‘Z’ may be written as 94Z.

1. What does the figure 4 indicate?
2. What does the figure 9 indicate?
3. What is the number of protons in atom Z?
4. What is the number of neutrons in atom Z?
5. What is the valency of atom Z?

Ans. 1. 4 is the atomic number of the element

2. 9 is the atomic mass of the element

3. The number of protons in atom Z = Atomic number = 4

4. The number of neutrons = Atomic mass – Atomic number = 9 – 4 = 5

5.The electronic configuration of Z = 2, 2

So, the valency of Z is 2

Q33.a)When a carpet is beaten with a stick, dust comes out of it. Explain.

b)Two objects of each of mass 1.5 kg, are moving in the same straight line but in the opposite direction. The velocity of each object is 2.5 m/s before the collision during which they stick together. What will be the velocity of the combined object after the collision?

Ans. a)Initially, carpet and dust particles both are in rest position but when the carpet is beaten by stick the carpet comes in motion but due to the inertia or first law of motion the dust particles resist to change their position so the dust particles detached from the carpet and hence comes out of the carpet.

b) The mass m of both objects is = 1.5 kg

The velocity of both objects  are given before collision = 2.5 m/s

Let the velocity of the combined object  after collision = v

The initial momentum of both objects = Final momentum of both objects

m1 u1 + m2 u= m1 v1 + m2 v2

If the velocity of one object is 2.5 m/s then the velocity of another object is = -2.5 because they are moving opposite to each other

1.5× 2.5 – 1.5× 2.5 = (1.5  + 1.5)v

3v = 0

v = 0

Hence the combined velocity of both object is 0 or they will come to in rest

Q34.a)Why is it difficult to hold a school bag having a strap made of a thin and strong string?

b)The volume of a 500 g sealed packet is 360 cm3. Will it sink or not if the density of water is 1gcm-3?

What will be the mass of the water displaced by this packet?

Ans. a) The relationship between thrust and pressure is P = F/A, where F is the thrust, P is pressure and A is the area. The school bag having a strap made of a thin strong string have a smaller area that increases pressure on the soldiers so it is difficult to hold.

b) The density of water is = 1 gcm-3

$\boldsymbol{Density =\frac{Mass}{Volume}}$

Mass of sealed packet = 500 g

The volume of sealed packet =360 cm3

$\boldsymbol{Density =\frac{500}{360}=1.39\: gcm^{-3}}$

The density of sealed packet > The density of water

Hence the sealed packet will sink in the water

The volume of water displaced by the sealed packet = The volume of  sealed packet = 360 cm3

Mass of water displaced by sealed packet = Density of water × The volume of water displaced by the sealed packet

$\boldsymbol{= 1\: gcm^{-3}\times 360\: cm^{3}=360\: g}$

Q35.a)Which causes more severe burns−boiling water or stream at the same temperature? Why ?

b)Differentiate between boiling and evaporation.

Ans.a) Since the latent heat of steam is more than the water and its kinetic energy is also higher so steam causes severe burns even in the condition when both temperatures is the same.

b) Boiling is the process which starts at a particular temperature of the liquid. Boiling occurs on the entire mass of the liquid. Bubbles are formed during the process of boiling. Boiling occurs when a liquid is given the heat.

Evaporation takes place at all temperature. Evaporation occurs on the surface of the liquid when it gets heat from the surroundings. Bubbles are not formed like boiling. Evaporation occurs naturally.

Q36.a)Give three features of cardiac muscles.

b)Draw a neat, well –labelled diagram of neuron.

Ans. a) Three features of cardiac muscles are following.

(i) Cardiac muscles are involuntary muscles and involve in rhythmic contraction and relaxation

(ii) Cardiac cells are cylindrical, elongated and of a single nucleus.

(iii) Cardiac cells are striated and grouped together through the intercalated disc that performs contractile functions of the heart.

b)

Q37.What is SONAR? How is it used to detect an underwater object and measure its distance?

Ans. SONAR stands for Sound Of Navigation And Ranging, it is used to detect the depth of the objects under the sea as following.

Let the depth of sea is = x and the speed of sound in water is = v

Time taken by the signal in returning back = t

Total distance covered by the signal = x + x = 2x

$\boldsymbol{Speed=\frac{Distance}{Time}}$

$\boldsymbol{v=\frac{2x}{t}}$

$\boldsymbol{x=\frac{vt}{2}}$

Hence x is the depth of sea or of an object under the sea.

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