CBSE Sample Papers for Class 9 Science Set 5 with Solutions

Students must start practicing the questions from CBSE Sample Papers for Class 9 Science with Solutions Set 5 are designed as per the revised syllabus.

CBSE Sample Papers for Class 9 Science Set 5 with Solutions

Time: 3 Hrs.
Max. Marks: 80

General Instructions :

• This question paper consists of 39 questions in 3 sections. Section A is Biology, Section B is Chemistry and Section C is Physics.
• All questions are compulsory. However, an internal choice is provided in some questions.
• A student is expected to attempt only one of these questions.

Section – A

Question 1.
Which of the following organelles helps in the manufacture of fat molecules and lipids?
(a) Lysosomes
(b) SER
(c) RER
(d) Golgi
Answer:
(b) SER

Explanation:
SER Smooth endoplasmic reticulum helps in the synthesis of fats and lipids in the cell.

Question 2.
Which of the following are correct statements related to plant tissues?
(i) Collenchyma cells are dead and provide flexibility.
(ii) Xylem is a complex permanent tissue made up of more than one type of cell.
(iii) Sclerenchyma cells have thin walls and large intercellular spaces.
(iv) Parenchyma helps in food storage and sometimes photosynthesis.
(v) Phloem transport water from roots to leaves.

(a) (i) and (ii)
(b) (ii) and (iv)
(c) (iii) and (iv)
(d) (iv) and (v)
Answer:
(b) (ii) and (iv)

Explanation:
The statements (ii) and (iv) are correct as xylem is a complex permanent tissue made of different cell types, and parenchyma helps in food storage and sometimes photosynthesis.

Question 3.
The plasma membrane is flexible and is made up of which of the following organic molecules?
(a) Lipids and proteins
(b) Proteins and cellulose
(c) Chitin and protein
(d) Proteins and pectin
Answer:
(a) Lipids and proteins

Explanation:
The plasma membrane is mainly made up of lipids and proteins, which provide flexibility and controls the movement of substances in and out of the cell.

Question 4.
Select the group in which all the tissues are of simple permanent type.
(a) Parenchyma, collenchyma, sclerenchyma
(b) Xylem, phloem, parenchyma
(c) Collenchyma, sclerenchyma, xylem
(d) Phloem, parenchyma, collenchyma
Answer:
(a) Parenchyma, collenchyma, sclerenchyma

Explanation:
Parenchyma, collenchyma and sclerenchyma belong to the same group as all of them are simple permanent tissues.

Question 5.
Which of the following is a method of increasing soil fertility naturally?
(a) Crop rotation
(b) Excessive use of chemical fertilisers
(c) Hybridisation
(d) Over-irrigation
Answer:
(a) Crop rotation

Explanation:
Crop rotation helps in maintaining soil fertility by growing different crops in a sequence, which prevents nutrient depletion.

Question 6.
Which of the following is a correct combination of cell organelle and its function?
(a) Mitochondria: Protein synthesis
(b) Ribosome: Energy production
(c) Lysosome: Digestion of waste materials
(d) Chloroplast: Storage of genetic material
Answer:
(c) Lysosome: Digestion of waste materials

Explanation:
Lysosome : Digestion of waste material is the correct combination as lysosomes contain digestive enzymes that help breakdown waste materials and old cell parts.

Question 7.
Which of the following crops is grown in the kharif season?
(a) Wheat
(b) Mustard
(c) Pea
(d) Maize
Answer:
(d) Maize

Explanation:
Maize is a kharif crop, sown at the beginning of the monsoon season.

The following two questions consists of two statements – Assertion (A) and Reason (R). Answer the questions by selecting the appropriate option given belozv.
(a) Both (A) and (R) are true and (R) is the correct explanationof (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Question 8.
Assertion (A) Plasma membrane is selectively permeable. [1]
Reason (R) Plasma membrane allows some molecules to pass through it more easily than others.
Answer:
(a) Both A and R are true and R is the correct explanation of A.

Question 9.
Assertion (A) Lining of the mouth have extremely thin and flat tissue. [1]
Reason (R) Tissues present in the lining of the mouth possess cilia that help in the movement of particles.
Answer:
(c) (A) is true, but (R) is false.

Explanation:
R can be corrected as Lining of mouth have simple squamous epithelial cells.

Question 10.
Plastids are called kitchen of the plant cell. Comment upon the statement with justification. [2]
Answer:
Plastids are called the kitchen of the plant cell because they are’involved in making and storing food. Chloroplasts, which are a type of plastid, contain chlorophyll that captures sunlight to carry out photosynthesis, producing food for the plant. Other plastids like leucoplasts store starch, oils and proteins, which are essential nutrients for the plant. Thus, plastids play an important role in food production and storage in plant cells.

Question 11.
Attempt either A or B. [2]
A. Plants have different types of meristematic tissues that help them in growth.
(i) Name any two types of meristematic tissues found in plants.
(ii) State one important function of each tissue you have named.
Answer:
(i) Two types of meristematic tissues found in plants are apical meristem and lateral meristem.
(ii) Apical meristem helps in the increase of length of the plant, while lateral meristem helps in the increase of thickness of the plant.

Or

B. Explain how the phloem transports food in plants.
Answer:
Phloem is responsible for transporting food from the leaves to other parts of the plant. The food moves through tube-like structures called sieve tubes. Companion cells help sieve tubes in the process by providing energy. This process is called translocation and is important for supplying nutrients to different parts of the plant.

Question 12.
Farmers use various plants and animals to increase food production and improve food resources. [2]
Explain how crops and animals help in this process.
Answer:
Farmers grow crops like wheat, rice and maize to provide food grains for people. Along with this, they rear animals such as cows, buffaloes and goats that supply milk, meat, and other products. The combined use of crops and animals helps to increase food production and meet the nutritional needs of the growing population. This way, both crop cultivation and animal husbandry play an important role in improving food resources.

Question 13.
Draw the structure of an eukaryotic cell and explain the role of golgi apparatus. [3]
Answer:
Role of golgi apparatus is as follows.
The golgi apparatus modifies proteins and lipids from the endoplasmic reticulum, then sorts and packages them into vesicles for transport within or outside the cell. This helps the cell process and distribute important molecules efficiently.

showing the structure of an eukaryotic cell

Question 14.
In an experiment, a biologist studied two types of animal tissues, muscular tissue and nervous tissue. [3]
(i) Name the main cell types found in these two tissues.
(ii) Explain how these tissues help in the functioning of the human body.
Answer:
(i) The main cell types found in muscular tissue are muscle fibers, which are long and capable of contracting. In nervous tissue, the main cells are neurons, which transmit electrical signals.
(ii) Muscular tissue helps in movement by contracting and relaxing, allowing body parts to move. Nervous tissue controls and coordinates body activities by sending messages from the brain and spinal cord to different parts of the body. Together, these tissues help the body to respond quickly to changes and perform various functions smoothly.

Question 15.
Neha studied animal tissues in her biology class. She observed that some tissues help in movement by contracting, while others help in transmitting messages across the body. She also learned that muscle tissue contains specialised cells that contract to produce movement and nervous tissue contains cells that carry electrical signals to coordinate body functions. [4]

Attempt either subpart A or B.
A. Name the two types of tissues Neha studied and differentiate between them.
Answer:
The two types of tissues Neha studied are muscular tissue and nervous tissue. Muscular tissue helps in movement by contraction, while nervous tissue transmits messages in the body.

Or
B. Explain the structure of skeletal muscle.
Answer:
Skeletal muscle is a voluntary muscle attached to bones. Its cells are long, cylindrical, unbranched, – and multinucleated. They have alternating light and dark bands called striations. These muscles contract and relax quickly, helping in movement of body parts under our conscious control.

C. Describe the structure of nervous tissue.
Answer:
Nervous tissue is made up of specialised cells called neurons. A neuron has a cell body with a nucleus and cytoplasm, long extensions called dendrites that receive messages and a single long fibre called the axon that carries messages away. Nervous tissue is found in the brain, spinal cord and nerves, and it helps in transmitting information rapidly between different parts of the body.

D. Identify the type of tissue shown in the picture given below and state its function.

Answer:
The given figure represents stratified squamous epithelial tissue. Stratified squamous epithelial tissue protects the underlying tissues in areas like the skin and mouth where there is a lot of friction.

Students should not confuse between simple epithelium and stratified squamous epithelium. Simple i epithelium has a single layer of cells, while stratified I squamous epithelium has multiple layers of cells.

Question 16.
Attempt either A or B. [5]
A. Rahul observed two fields on his farm. In field A, he grew wheat continuously for many years. In field B, he practiced crop rotation by growing wheat one season and legumes the next.
(i) Which field do you think has better soil fertility? Give reason.
(ii) How does crop rotation help in improving soil fertility?
Answer:
(i) Field B has better soil fertility because growing different crops like wheat and legumes alternately helps maintain nutrients in the soil.
(ii) Crop rotation improves soil fertility by allowing legumes to fix nitrogen in the soil, which replenishes nutrients and reduces soil exhaustion.

To obtain maximum marks students can explain that crop rotation also increases the soil fertility.

Or

B. Aniket has two fields. In field A, he waters the crops regularly at fixed intervals, while in field B, he waters the crops irregularly depending on rainfall.
(i) Which field is likely to have better crop growth? ‘
(ii) How does regular irrigation help in increasing food production?
Answer:
(i) Field A is likely to have better crop growth than field B because regular wattering provides plants with the right amount of water at proper intervals.
(ii) Regular irrigation helps increase food production by providing sufficient water to crops, which supports their growth and improves yield even during dry periods or irregular rainfall. Proper irrigation supports healthy plant growth, improves crop yield, and allows farmers to grow crops througout the year, leading to better food availability and income.

Section – B

Question 17.
Which one of the following changes is different from the remaining three? [1]
(a) Conversion of milk into cheese
(b) Making of bread from wheat flour
(c) Distillation of water
(d) Reacting zinc metal with dilute hydrochloric acid
Answer:
(c) Distillation of water

Explanation:
Among the given changes all are chemical changes except (c), i.e., distillation of water.

Question 18.
Four statements about subatomic particles are listed below. [1]
I. Electrons are negatively charged particles present outside the nucleus.
II. Protons are neutral particles located in the nucleus of an atom.
III. The mass of a neutron is slightly more than that of a proton.
IV. The number of protons in an atom is equal to the number of electrons in a neutral atom.

Which statements are correct?
(a) I and II
(b) II and III
(c) I, III and IV
(d) I, II and III
Answer:
(c) I, III and IV

Explanation:
Statement I and IV are true for a neutral atom, and III is correct as the neutron is slightly heavier than the proton. Statement II is incorrect because protons are positively charged, not neutral.

Question 19.
The best evidence for the existence and movement of particles in liquids was provided by [1]
(a) kerosene
(b) krypton
(c) carbon steel
(d) carbon dioxide
Answer:
(a) kerosene

Explanation:
The best evidence for-the existence and movement of particles in liquids was provided by kerosene.

Question 20.
Which of the following solutions shows the Tyndall effect? [1]

Solution	Solute	Solvent
(a)	Chalk	Water
(b)	Sugar	Water
(c)	Iodine	Alcohol
(d)	Starch	Water

Answer:
(d) Starch dissolved in water shows a Tyndall effect because it forms a colloidal solution when dispersed in water.

Question 21.
When the atomic number of an element is increased by one, the change observed in the atom is because [1]
(a) the number of protons decreases by one.
(b) one proton and one electron are added to the atom.
(c) only one neutron is added to the nucleus.
(d) one electron is removed from the atom.
Answer:
(b) one proton and one electron are added to the atom.

Explanation:
Atomic number represents the number of protons in an atom. Increasing the atomic number by one means one more proton (and to maintain neutrality, one electron) is added.

Question 22.
The formula of chloride of a metal M is MCl₃, then the formula of the phosphate of metal M will be [1]
(a) M₂PO₄
(b) MPO₄
(c) M₂(PO₄)₃
(d) M₃PO₄
Answer:
(b) MPO₄

Explanation:

The formula of phosphate of metal M will be MPO₄.

Question 23.
Two samples, ‘A and’ B’, are taken for testing. Sample ‘A is a foam used in shaving cream, and sample’ B is milk. Which of the following classification is correct? [1]
(a) Sample ‘A is a solid sol and sample’B’ is an emulsion.
(b) Sample ‘A’ is a foam (gas in liquid) and sample ‘B’ is a gel (liquid in solid).
(c) Sample ‘A’ is a foam (gas in liquid) and sample ‘B’ is an emulsion (liquid in liquid).
(d) Sample ‘A is an emulsion and sample ‘B’ is a sol (solid in liquid).
Answer:
(c) Sample ‘A’ is a foam (gas in liquid) and sample ‘B’ is an emulsion (liquid in liquid).

Explanation:
In foams like shaving cream, gas is dispersed in a liquid medium. Milk is an emulsion where liquid fat droplets are dispersed in water.

The following question consists of two statements – Assertion (A) and Reason (R). Answer the question by selecting the appropriate option given below :
(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Question 24.
Assertion (A) Magnesium ion and chloride ion combine to form a compound having chemical formula MgCl2. [1]
Reason (R) Magnesium ion and chloride ion contains +1 and -2 charges, respectively.
Answer:
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).

Explanation:
The correct form of (R) is magnesium and chloride ions contain +2 and -1 charges, respectively.

Question 25.
The below figure represents the electron distribution of an unknown atom. If the number of protons is 8, then [2]

(a) what is the atomic number of the atom?
(b) what is the charge on the atom?
Answer:
(a) Atomic number = Number of protons
Since, the number of protons is 8.
So, the atomic number is also 8.

(b) The charge on the atom is zero because the number of electrons and the number of protons are equal.

Question 26.
Attempt either A or B [3]
A. Classify each of the following as a homogeneous or heterogeneous mixture.
(a) Soda water
(b) Wood
(c) Filtered tea
Answer:
Homogeneous mixture has uniform composition while heterogeneous mixture has non-uniform composition.
(a) Soda water Homogeneous mixtur
(b) Wood Fleterogeneous mixture
(c) Filtered tea Homogeneous mixture

Or

B. Which of the following materials fall into the category of ‘pure substance’?
(a) Mercury
(b) Milk
(c) Iron
Answer:
Pure substance These substance are made up of only one kind of particle and have a fixed or constant composition.
(a) Mercury Pure substance
(b) Milk It is a mixture of water, milk, protein and fat. It is not a pure substance.
(c) Iron Pure substance

Question 27.
Consider the diagram given below [3]

(a) Identify A and Bin the given diagram.
(b) What is the role of the cotton plug in the above shown experiment.
(c) Which physical process is explained through the above figure?
Answer:
(a) ‘A ‘ is ammonium chloride vapours and ‘ B’ is ammonium chloride in solidified form.
(b) The above figure represents sublimation. Hence, a loose cotton plug is placed in the upper open end of the funnel to prevent the ammonium chloride vapour from escaping into the atmosphere. So that solid ammonium chloride can be collected.
(c) The above figure represents the sublimation of ammonium chloride. Sublimation is a physical process in which a solid is directly converted into gaseous form without first converting into liquid state.

Question 28.
After the discovery of sub-atomic particles like electrons and protons, it was important to understand where these particles are located within the atom, i.e., what is the model of an atom? Different models have been put forward from time to time like Thomson’s model, Rutherford’s model, Bohr’s model etc. Bohr’s model gave a clear picture of how the electrons are distributed around the nucleus in different shells. [4]
A. Which of the following figures do not represent Bohr’s model of an atom correctly?

Answer:
Figures (b) and (d) do not correctly represent the Bohr’s model of an atom. It is because the maximum number of electrons in the K(I) shell is 2 and not 4. So (b) is wrong and the maximum capacity of the £.(11) shell is 8 electrons, not 9. So, (d) is also wrong.

B. Write any one postulate of the model proposed by J.J. Thomson.
Answer:
Electrons are embedded in the sphere of positive charge of an atom.

Or

Why did Rutherford select a gold foil in his a-ray scattering experiment?
Answer:
Rutherford selected a gold foil in his a-ray scattering experiment because gold is the most malleable metal and can be easily made into very thin sheets.

C. What are canal rays? Which of the following is true and why? The electrical neutrality of an atom in Thomson’s model is because
(a) the number of electrons is greater than the positive charge.
(b) negative charges are scattered randomly outside the nucleus.
(c) equal number of positive and negative charges balance each other.
(d) positive charge is concentrated at the center of the atom.
Answer:
Canal rays or anode rays are the positively charged rays which are seen moving from the anode towards cathode in a specially designed discharge tube, when a high voltage is applied across the electrodes.

The correct option is (c): equal number of positive and negative charges balance each other. According to Thomson model, an atom consists of a positively charged sphere and the electrons are embedded in it. The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.

Question 29.
Attempt either A or B [5]
A. Five ions/elements 1, 2, 3, 4 and 5 are given as
1. Chloride
2. Sulphide
3. Nitride
4. Phosphate
5. Sulphite
(a) Arrange the given ions/elements in the increasing order of their valency.
Answer:
The given five ions/elements are
1. Chloride → 1 valency
2. Sulphide → 2 valency
3. Nitride → 3 valency
4. Phosphate → 3 valency
5. Sulphate → 2 valency
The increasing order of their valency is
1 < 2 = 5 < 3 = 4

Don’t make mistake in arranging the elements if you do not know about the exact valencies.

(b) Identify two of the sulphur ions from the above given ions/elements.
Answer:
From the given ions, two of the sulphur ions are sulphide and sulphite.

(c) Explain their atomicity with symbol representation.
Answer:

Non-metallic element	Symbols	Atomicity
1.	Cl–	Monoatomic
2.	S2-	Monoatomic
3.	N3-	Monoatomic

(d) What are ions?
Answer:
Compounds composed of metals and nonmetals contain charged species. The charged species are known as ions.

(e) What are the types of ions?
Answer:
An ion can be of two types i.e., negatively or positively charged. A negatively charged ion is called an ‘anion’ and the positively charged ion, is called ‘cation’.

Or

B. The given figure shows the symbols for some elements as proposed by John Dalton in the early 19th century. Answer the following questions based on the figure.

Based on the information given above, answer the following questions.
(a) Name the element shown in the figure whose modem symbol exactly matches Dalton’s symbols.
(b) Identify the element that is represented by a circle with an inner dot in Dalton’s symbols.
(c) Explain why Dalton proposed these types of symbolic representations for elements.
(d) What was Berzilius’ suggestion on atomic symbols of elements?
(e) Name the elements X, Y, Z in the figure whose Dalton symbols are given in the last row.
Answer:
(a) The element whose modem symbols match Dalton’s symbols is oxygen (O).
(b) The element represented by a circle with a central dot is hydrogen.
(c) Dalton proposed these symbolic representations to provide a visual method of identifying elements and their combinations in compounds. These symbols helped in representing atoms in chemical reactions in a simple and memorable way during his time.
(d) Berzilius suggested that the symbols of elements be made from one or two letters of the name of the element.
(e) The name of the elements X, Y, Z in the last row according to Dalton’s symbols are gold, platinum, and mercury respectively.

Section – C

Question 30.
Consider uniformly accelerated motion. , [1]
I. v = u + at is valid for constant acceleration.
II. Average velocity = \(\frac{u+v}{2}\) only when acceleration is constant.
III. s = ut + \(\frac{1}{2}\) at holds even if acceleration varies with time.

Choose the correct option.
(a) I and III
(b) I and II
(c) II and III
(d) I, II and III
Answer:
(b) I and II

Explanation:
It is true: v = u + at requires constant acceleration. II is true: v = \(\frac{(u+v)}{2}\) holds only when acceleration is constant. III is false:
s = ut + \(\frac{1}{2}\) at is valid only for constant acceleration.

Question 31.
Choose the correct option that explains why two sounds with same amplitude but different frequencies are perceived as different pitches? [1]
(a) Frequency determines pitch higher frequency is heard as higher pitch.
(b) Amplitude determines pitch, frequency determines loudness.
(c) Pitch depends only on medium, not on frequency.
(d) Human ear cannot distinguish different frequencies if amplitudes are same.
Answer:
(a) Frequency determines pitch higher frequency is heard as higher pitch.

Explanation:
Frequency determines pitch: a higher frequency is heard as a higher pitch. Amplitude affects loudness, not pitch.

The following question consist of two statements – Assertion (A) and Reason (R). Answer the question by selecting the appropriate option given below.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Question 32.
Assertion (A) In a longitudinal sound wave, compressions are regions of higher pressure and rarefactions are regions of lower pressure. [1]
Reason (R) Particle crowding in compressions increases local density and pressure, while spreading in rarefactions reduces them.
Answer:
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).

Explanation:
Compressions have high pressure and rarefactions have low pressure due to particle crowding and spreading. Hence, Both (A) and (R) are true and (R) is the correct explanation of (A).

Question 33.
Ablock of mass 6 kg is kept on the surface of the Earth. Take acceleration due to gravity on Earth gE = 9.8 m/s². The acceleration due to gravity on the Moon is gM = \(\frac{1}{6}\) yE.
(i) Identify the physical quantities involved in this situation.
(ii) State clearly the difference between mass and weight.
(iii) Calculate the weight of the block on (a) the Earth and (b) the Moon. Give answers with units.
Answer:
(i) Physical quantities involved
Mass of block (m)
Weight of block (W)
Acceleration due to gravity (gE, gM) [VSs]

(ii) Difference between mass and weight
Mass is the amount of matter in a body, and is intrinsic, remaining constant everywhere. Its unit is kilogram (kg).
Weight is the gravitational force acting on the body and depends on the local acceleration due to gravity. Its unit is newton (N).

(iii) Given
m = 6 kg, gE = 9.8 m/s², gM = \(\frac{1}{6}\)gE.
(a) Weight on Earth:
W_E = mgE = 6 × 9.8 = 58.8N.
Weight on Moon:
gm = \(\frac{9.8}{6}\) = 1.633 m/s², so
W_M = mgM= 6 × \(\frac{9.8}{6}\) = 9.8 N
So, the block’s weight on the Moon is one-sixth of its weight on Earth.

Question 34.
Attempt either A or B.

A. The velocity-time graph of a body moving in a straight line is shown figure
(i) Calculate the acceleration of the body.
(ii) If the mass of the body is 2 kg, determine the force acting on it.
Answer:
(A) From the graph: initial velocity u = 25 m / s at t = 0
and final velocity = 0 m / s at t = 10s
(i) Acceleration a = \(\frac{v-u}{t}=\frac{0-25}{10}\) = -2.5 m/s
(The negative sign shows the body is decelerating which means acceleration is opposite to the direction of motion.)

(ii) Net force on the body (mass m = 2 kg)
F = ma = 2 × (- 25) = -5 N

Mention initial velocity, final velocity and time from the graph before calculating acceleration and force.

Or

B. The image shows a table with a book placed on it
(i) Identify the action-reaction pairs shown in the diagram.
(ii) Explain how Newton’s third law of motion applies to the forces acting on the book and the table? [3]
Answer:
(i) X and Y.
(ii) According to Newton’s third law of motion, every action has an equal and opposite reaction, the book exerts a downward force (its weight) on the table. The table exerts an equal upward normal force on the book.

Question 35.

(i) Identify whether the wave is longitudinal or transverse.
(ii) A child drops a stone into a still pond, producing ripples that are 20 cm apart. If 25 ripples pass by a fixed point in 15 seconds, how long will it take for the disturbance to travel 6 m across the pond? [3]
Answer:
(i) The disturbance is shown perpendicular to the time axis, the wave is transverse.

(ii) Given
Wavelength, λ = 20 cm = 0.20 m
Number of ripples passing in 15 s = 25 Frequency,
f = \(\frac{\text { Number of ripples }}{\text { time }}=\frac{25}{15}\) = 1.67 Hz
Wave speed: v = f × λ = 1.67 × 0.20 = 0.334 m/s
Time to travel 6 m
t = \(\frac{\text { Distance }}{\text { Speed }}=\frac{6}{0.334}\)
So, the disturbance will take 18 seconds to travel 6 m across the pond.

Question 36.
A newly discovered spherical planet has the same mean density as Earth but twice Earth’s radius.
(Take g Earth 9.8 m/s2). [3]
(i) Find the acceleration due to gravity on the surface of this planet.
(ii) If a person weighs 600 N on Earth, find their weight on this planet.
Answer:
Given,
Density of planet = Density of Earth
Radius of planet R_p = 2R_E
g_E = 9.8 m/s²
Weight on Earth W_E = 600 N

(i) Acceleration due to gravity on planet
We know for a spherical planet: g = \(\frac{G M}{R^2}\)
But mass M = ρ × \(\frac{4}{3}\)nR³ , so: g ∝ ρR

If density ρ is same, \(\frac{g_p}{g E}=\frac{R_p}{R_E}\)
\(\frac{g_p}{9.8}=\frac{2 R_E}{R_E}\)
g_p = 2 × 9.8 = 19.6 m/s²

(ii) Weight on planet
Weight W = mg

Mass of person m = \(\frac{W_E}{g E}=\frac{600}{9.8}\) ≈ 61.22 kg
Weight on planet: W_p = m × g_p = 61.22 × 19.6
≈ 1200 N

Question 37.
Abullet of mass 20 g is fired horizontally into a wooden block and comes to rest after penetrating 0.04 m into it. [3]

(i) State Newton’s second law of motion in words.
(ii) If the initial velocity of the bullet was 400 m/s, calculate the average retarding force exerted by the block on the bullet.
Answer:
(i) Newton’s second law states that the rate of change of momentum of a body is directly proportional to the applied force and this change takes place in the direction of the applied force.
(ii) Given:
m = 20 g = 0.02 kg
u = 400 m/s, v = 0, s = 0.04 m
Find acceleration using equation of motion:
v² = u² + 2as
0 = (400)² + 2 × a × 0.04
0 = 160000 + 0.08a
a = \(\) = -2.0 × 10⁶ m/s²
Force using F = m × a
F = 0.02 × (-20 × 10⁶)
F = -40,000 N
Average retarding force = 40,000 N (opposite to motion).

Question 38.
The graph below shows tire positions of a body at different time intervals, while travelling from his home to school in the morning. Based on the given graph, answer the following questions. [4]

A. Calculate the speed of the body as it moves from A to B and B to C.
B. Find the time interval during which speed is maximum.
Attempt either subpart C or D
C. Determine the distance covered between B to C.
D. Is the motion of the boy during time interval from A to D is uniform?
Answer:
A. For the motion from point A to B
Time taken, t = 5 – 2 = 3s
Distance covered = 3 m
∴ Speed will be during point A to B
= \(\frac{\text { Distance }}{\text { Time }}=\frac{3}{3}\) = 1 m/s

Similarly, for the motion from point B to C
Time taken, = 7 – 5 = 2 s
Distance covered = 0 m
∴ Speed = \(\frac{\text { Distance }}{\text { Time }}=\frac{0}{3}\) = 0m/s = 0

B. Speed in the’interval C to D,
Time taken = 3 s
Distance covered = 8 – 3 = 5 m
Speed will be during point C to D
= \(=\frac{\text { Distance }}{\text { Time }}=\frac{5}{3}\) = 166 m/s
Speed is maximum from point C to D.

C. Body does not change its position from B to C. So, distance covered is zero.
Or
D. No, boy is moving with different speed at different time interval.

Question 39.
Attempt either A or B [5]
A. A car of mass 800 kg starts from rest and accelerates to a speed of 18 m/s after covering a distance of 100 m on a straight road.
(i) How much work is done by force applied to the car to increase its speed?
(ii) What is the change in the car’s kinetic energy during this motion?
(iii) If the car moving on a frictions surface, would the work done change? Why or why not?
Or
B. A ball of mass 2 kg is thrown vertically upward with a speed of 10 m/s. Takeg = 10m/s2.
(i) Calculate the kinetic energy of the ball at the point of projection.
(ii) Calculate the maximum height reached by the ball.
(iii) Find the potential energy of the ball at half of its maximum height.
Answer:
A. (i) Given,
Mass of the car, m = 800 kg
Final velocity, v = 18 m/s
Initial velocity, u = 0 m/s (since the car starts from rest)
Distance travelled, s = 100 m
The work done by the applied force is equal to the change in kinetic energy:
W = AKE = KE_final – KE_initial

Kinetic energy at the final velocity:
KE_final = \(\frac{1}{2}\) mv²
= \(\frac{1}{2}\) × 800 × (18)²
= 129600 J
Kinetic energy at the initial velocity (at rest)
KE_initial = 0 J
Work done W = 129600 – 0 = 129600 J
So, the work done by the applied force is 129600 J.

(ii) The change in kinetic energy is simply the difference between the final and initial kinetic energies:
AK E = KE_final – KE_initial
= 129600 – 0
= 129600J
So, the change in kinetic energy is 129600 J.

(iii) On a frictionless surface, the car would not lose any energy due to friction, so the work done by the applied force would still be the same:
The work done would remain 129600 J, as the energy would be used entirely to increase the car’s kinetic energy.

Or

B. (i) Given, mass = 2 kg
speed = 10 m/s g = 10 m /s2
Kinetic Energy:
KE = \(\frac{1}{2}\)mv²
= \(\frac{1}{2}\) × 2 × (10)²
= 100 J

(ii) At maximum height, KE = 0 and all energy is potential:
mgh = 100
2 × 10 × h = 100
h = 5 m

(iii) Half the height = \(\frac{h}{2}=\frac{5}{2}\) = 2.5m
Potential Energy:
PE = mgh = 2 × 10 × 25
= 50 J

Students often assume half the height means half the energy-but energy distribution changes with speed.