Half Yearly Class 9 Science Set 3 (Solutions)

Time: 3 Hours
Maximum Marks: 80
General Instructions:
(i) The question paper comprises four sections: A, B, C, and D. 
(ii) All questions are compulsory. However, internal choices are provided in some questions. 
(iii) Section A consists of 20 objective type questions (MCQs/Assertion-Reason) carrying 1 mark each. 
(iv) Section B consists of 7 very short answer questions carrying 2 marks each. 
(v) Section C consists of 7 short answer questions carrying 3 marks each. 
(vi) Section D consists of 5 long answer questions carrying 5 marks each.
(vii) Draw neat and labelled diagrams wherever necessary.

Syllabus: The half-yearly question paper is framed from the following chapters: Matter in our surroundings, Is matter around us  pure?, Fundamental unit of life, tissues, Motion, Forces and laws of Motion.

Section A

Q1. The change of a liquid into a gas at any temperature is called:   (1 Mark) 
(a) Boiling 
(b) Evaporation 
(c) Sublimation 
(d) Condensation 

Ans: (b)
Sol: Evaporation is the process where a liquid changes to a gas at any temperature from its surface.

Q2. Which of the following is an element?   (1 Mark) 
(a) Water 
(b) Air 
(c) Oxygen 
(d) Salt 

Ans: (c)
Sol: Oxygen is an element, as it consists of only one type of atom.

Q3. The organelle that controls all cell activities is:   (1 Mark) 
(a) Mitochondria 
(b) Nucleus 
(c) Ribosome 
(d) Lysosome 

Ans: (b)
Sol: The nucleus controls all cell activities by regulating gene expression.

Q4. Which plant tissue conducts food?   (1 Mark) 
(a) Xylem 
(b) Phloem 
(c) Sclerenchyma 
(d) Collenchyma 

Ans: (b)
Sol: Phloem conducts food (sugars) in plants.

Q5. An object moving with constant speed in a straight line has:   (1 Mark) 
(a) Uniform acceleration 
(b) Non-uniform acceleration 
(c) Zero acceleration 
(d) Negative acceleration 

Ans: (c)
Sol: Constant speed in a straight line implies no change in velocity, so acceleration is zero.

Q6. The unit of momentum is:   (1 Mark) 
(a) N 
(b) kg m/s 
(c) m/s² 
(d) J 

Ans: (b)
Sol: Momentum is mass times velocity, with the unit kg m/s.

Q7. Which of the following is a colloid?   (1 Mark) 
(a) Sugar solution 
(b) Milk 
(c) Salt solution 
(d) Pure water 

Ans: (b)
Sol: Milk is a colloid, with fat globules dispersed in water.

Q8. The organelle that helps in packaging proteins is:   (1 Mark) 
(a) Nucleus 
(b) Mitochondria 
(c) Golgi apparatus 
(d) Lysosome 

Ans: (c)
Sol: The Golgi apparatus packages proteins for transport within or outside the cell.

Q9. The slope of a velocity-time graph gives:   (1 Mark) 
(a) Distance 
(b) Displacement 
(c) Speed 
(d) Acceleration 

Ans: (d)
Sol: The slope of a velocity-time graph represents acceleration.

Q10. Newton's first law of motion is also known as:   (1 Mark) 
(a) Law of acceleration 
(b) Law of inertia 
(c) Law of action-reaction 
(d) Law of momentum 

Ans: (b)
Sol: Newton's first law is also called the law of inertia.

Q11. Assertion (A): Liquids have a definite volume but no definite shape.   (1 Mark) 
Reason (R): Liquid particles are loosely packed and can flow. 
(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. 

Ans: (a)
Sol: Liquids take the shape of the container due to loosely packed particles that allow flow.

Q12. Assertion (A): A compound has a fixed composition.   (1 Mark) 
Reason (R): The components of a compound are chemically combined in a definite ratio. 
(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. 

Ans: (a)
Sol: A compound has a fixed composition due to chemical bonding in a definite ratio.

Q13. Assertion (A): Chloroplasts are found only in plant cells.   (1 Mark) 
Reason (R): They contain chlorophyll for photosynthesis. 
(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. 

Ans: (a)
Sol: Chloroplasts, containing chlorophyll, are found only in plant cells for photosynthe- sis.

Q14. Assertion (A): Bone is a connective tissue.   (1 Mark) 
Reason (R): It provides structural support to the body. 
(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. 

Ans: (a)
Sol: Bone is a connective tissue that provides structural support.

Q15. Assertion (A): A body can have different distances but the same displacement.   (1 Mark) 
Reason (R): Displacement is the shortest distance between initial and final positions. 
(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. 

Ans: (a)
Sol: Displacement depends only on initial and final positions, allowing different distances for the same displacement.

Q16. Assertion (A): Force can change the speed of an object.   (1 Mark) 
Reason (R): Force causes acceleration, which changes velocity. 
(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. 

Ans: (a)
Sol: Force causes acceleration, which changes the speed of an object.

Q17. Which of the following is a physical change?   (1 Mark) 
(a) Cooking of food 
(b) Freezing of water 
(c) Burning of wood 
(d) Rusting of iron 

Ans: (b)
Sol: Freezing of water is a physical change as it involves a change in state without chemical alteration.

Q18. The function of mitochondria in a cell is to:   (1 Mark) 
(a) Store waste 
(b) Produce energy 
(c) Synthesize proteins 
(d) Control cell division 

Ans: (b)
Sol: Mitochondria produce energy in the form of ATP through cellular respiration.

Q19. A body starts from rest and moves with an acceleration of 5 m/s² for 4 seconds. The distance covered is:  (1 Mark)  
(a) 20 m 
(b) 40 m 
(c) 60 m 
(d) 80 m 

Ans: (b)
Sol: Distance: s = ut + 1/2 at² = 0 + 1/2 × 5 × 4²  = 40 m.

Q20. The process used to separate a mixture of sand and water is:   (1 Mark) 
(a) Filtration 
(b) Distillation 
(c) Centrifugation 
(d) Sublimation

Ans: (a)
Sol: Filtration separates sand from water as sand particles are insoluble and larger.

Section B

Q1. Define latent heat of vaporization.  (2 Marks) 

Ans: Latent heat of vaporisation: The amount of heat energy required to change 1 kg of a liquid into a gas at its boiling point without a change in temperature.

Q2.  What is a pure substance? Give one example.  (2 Marks) 

Ans: Pure substance:  A substance with a fixed composition and definite properties. 
Example: Pure water.

Q3. Name two types of connective tissues in animals.  (2 Marks) 

Ans: Two types of connective tissues: Bone, Blood.

Q4.  What is the role of sclerenchyma in plants?  (2 Marks) 

Ans: Role of sclerenchyma: Sclerenchyma provides mechanical strength and support to plants due to its thick, lignified cell walls.

Q5. Define acceleration with an example.  (2 Marks) 

Ans: Acceleration: The rate of change of velocity per unit time.   
Example: A car increasing its speed from 20 km/h to 40 km/h in 5 seconds.

Q6.  State Newton's third law of motion.  (2 Marks) 

Ans: Newton's third law: For every action, there is an equal and opposite reaction.

Q7. What will happen if the apical meristem is damaged or cut?  (2 Marks) 

Ans: Apical meristems are present at the tips of roots, shoots, branches, and leaves. They form the growing parts of the roots and stems. If the apical meristem is damaged or cut, the growth in length of that plant part will gradually stop.

Section C

Q1.  We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert. (3 Marks)

Ans: This difference arises from the varying strength of the force of attraction between particles in gases versus solids. Air is a gas where the particles have the minimum force of attraction between them, allowing the particles to be easily separated. In contrast, a solid block of wood has particles held together with the maximum force of attraction. This force keeps the solid particles tightly together, making it rigid and difficult to change its shape or break through.

Q2. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature. (3 Marks) 

Ans: 

1. Identify the components and masses:

Mass of solute (Sodium Chloride) = 36 g (given in query)

Mass of solvent (Water) = 100 g (given in query)

2. Calculate the mass of the solution:

The mass of the solution is the sum of the mass of the solute and the mass of the solvent.

Mass of solution = Mass of solute + Mass of solvent

Mass of solution = 36 g + 100 g = 136 g

3. Calculate the concentration (Mass by Mass Percentage):

Concentration = (Mass of solute / Mass of solution) × 100

Concentration = (36 g / 136 g) × 100

Concentration ≈ 26.47%

The concentration of the saturated sodium chloride solution at 293 K is approximately 26.47%.

Q3. Draw a labelled diagram of a neuron.  (3 Marks) 

Ans: 

Q4.  Differentiate between xylem and phloem in plants (three points).  (3 Marks) 

Ans:  

Q5. Derive the third equation of motion: v² = u²  + 2as.  (3 Marks) 

Ans: Derivation of third equation of motion:
From first equation: v = u + at.
From second equation: (since average velocity = (u + v)/2).
Multiply both sides by 2: 2s = (u + v)t.
From v = u + at, we get t = (v - u)/a.
Substitute t in 2s = (u + v)t: 2s = (u + v)
Thus, v² = u² + 2as.

Q6. When will you say a body is in (i) uniform acceleration? (ii) nonuniform acceleration?  (3 Marks) 

Ans: 

A body is described as being in uniform acceleration or non-uniform acceleration based on how its velocity changes over time.

(i) Uniform Acceleration

You will say a body is in uniform acceleration when it travels in a straight line and its velocity increases or decreases by equal amounts in equal intervals of time.

• For all uniformly accelerated motion, the velocity-time graph is a straight line.

• The motion of a freely falling body is an example of uniformly accelerated motion.

(ii) Non-uniform Acceleration

You will say a body is in non-uniform acceleration if its velocity changes at a non-uniform rate.

• If a car traveling along a straight road increases its speed by unequal amounts in equal intervals of time, the car is said to be moving with non-uniform acceleration.

• In the case of non-uniformly accelerated motion, velocity-time graphs can have various shapes that are not a straight line

Q7. (Internal Choice)   (3 Marks) 
Option 1:  (i) What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
(ii)  What can you say about the motion of an object if its speed- time graph is a straight line parallel to the time axis?
Option 2:  Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?

Ans: Option 1: 
(i) If an object's distance-time graph is a straight line parallel to the time (x) axis, it means the position (distance along the y-axis) of the object is not changing as time passes. This indicates that the object is at rest or stationary

(ii) If an object's speed-time graph (or velocity-time graph) is a straight line parallel to the time (x) axis, it means the velocity of the object is constant.

• This indicates that the object is moving with uniform velocity or constant speed.

• The height of the velocity-time graph does not change with time.

• An object moving with uniform velocity has zero acceleration
OR Option 2:  

1. Falling Forward (Braking): When the moving bus brakes, the bus and your feet slow down instantly. However, the rest of your body, due to its inertia, tends to continue in the previous state of motion (forward velocity), causing you to lurch forward relative to the bus.

2. Falling Backwards (Accelerating): When the bus starts suddenly from rest, the bus and your feet are abruptly brought into motion. The rest of your body, due to its inertia, tends to remain in its initial state of rest, opposing the forward motion and causing you to fall backward

Section D

Q1. (a) Explain the process of freezing and factors affecting it. (3 marks) 
(b) A gas exerts pressure on the walls of the container. Give Reason. (2 marks) 

Ans: (a)  Freezing is the physical process where a liquid changes into a solid by losing heat energy at a specific temperature known as its freezing point. This process is the reverse of melting. When heat is removed from the liquid, the kinetic energy of its constituent particles decreases. As the particles slow down, the force of attraction between them overcomes their kinetic movement, causing the particles to leave their fluid state and lock into fixed positions (crystal lattice), resulting in a rigid solid structure.

Factors Affecting Freezing

The key factors influencing the freezing process are:

1. Temperature: A lower temperature increases the freezing rate, as more heat energy is lost rapidly from the substance.

2. Impurities: The presence of impurities generally acts to lower the freezing point of the liquid.

3. Pressure: Increased pressure may also lower the freezing point of a substance, which is particularly notable in water

(b) A gas exerts pressure because its particles move about randomly at high speed. Due to this high-speed random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is the force exerted by the gas particles per unit area on the walls of the container

Q2. (a) Describe the structure and functions of lysosomes in a cell. (3 marks) 
(b) Differentiate between prokaryotic and eukaryotic cells (any four points). (2 marks) 

Ans: 

(a) Structure and Functions of Lysosomes

Lysosomes are structurally defined as membrane-bound sacs filled with powerful digestive enzymes. These enzymes are manufactured by the Rough Endoplasmic Reticulum (RER).

Lysosomes function primarily as the waste disposal system of the cell. Their key functions include:

1. Digestion: They help keep the cell clean by digesting foreign materials entering the cell, such as bacteria or food, and breaking down waste materials and worn-out cell organelles into simpler substances.

2. Suicide Bags: They are also known as the 'suicide bags' of a cell. This term is used because, if the cell gets damaged or during disturbances in cellular metabolism, lysosomes may burst and their enzymes digest the cell's own contents. They are involved in cell recycling.

(b) Differentiate between Prokaryotic and Eukaryotic Cells 

Q3. (Internal Choice) 
Option 1:  (i)A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because (a) the batsman did not hit the ball hard enough. (b) velocity is proportional to the force exerted on the ball. (c) there is a force on the ball opposing the motion. (d) there is no unbalanced force on the ball, so the ball would want to come to rest. (3 Marks)
(ii) When a carpet is beaten with a stick, dust comes out of it, Explain. (2 Marks)
Option 2: An object of mass 1 kg travelling in a straight line with a velocity of 10 m s-1 collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.

Ans: Option 1:  (i) The correct option is (c) there is a force on the ball opposing the motion.

The ball slows down and comes to rest because an unbalanced force acts on it, opposing its forward motion. This force is primarily the force of friction, which always opposes the motion of objects.

If there were no unbalanced force acting on the ball, it would continue moving with uniform velocity (keep rolling forever), according to Newton's First Law of Motion. However, in practical situations, the frictional force acting opposite to the direction of motion causes the ball to stop after travelling some distance.
(ii) This phenomenon is explained by Inertia, which is codified in Newton's First Law of Motion.

1. Initial State: The carpet and the dust particles embedded in it are initially in a state of rest.

2. Action: The stick applies a sudden, unbalanced force that sets the carpet abruptly into motion.

3. Inertia: The dust particles, due to their inertia, resist this sudden change and tend to remain in their state of rest.

4. Result: Since the carpet moves away while the dust remains stationary, the particles are separated and come out of the carpet.
OR 
Option 2:
Momentum (p) is calculated as the product of an object's mass (m) and velocity (v):

p = m × v

The SI unit of momentum is kg·m·s⁻¹.

1. Total Momentum Just Before Impact

Momentum before impact (P_before) is the sum of the momentum of the object (p₁) and the stationary wooden block (p₂):

P_before = (m₁ × u₁) + (m₂ × u₂)

• Mass of object (m₁): 1 kg
• Initial velocity of object (u₁): 10 m·s⁻¹
• Mass of block (m₂): 5 kg
• Initial velocity of block (u₂): 0 m·s⁻¹

P_before = (1 kg × 10 m·s⁻¹) + (5 kg × 0 m·s⁻¹)

P_before = 10 kg·m·s⁻¹ + 0 kg·m·s⁻¹

P_before = 10 kg·m·s⁻¹

The total momentum just before the impact is 10 kg·m·s⁻¹.

2. Total Momentum Just After Impact

According to the Law of Conservation of Momentum, the total momentum remains unchanged after the collision if no external force acts on the system.

The total momentum just after the impact (P_after) is equal to the total momentum just before the impact:

P_after = P_before = 10 kg·m·s⁻¹

3. Velocity of the Combined Object

After the collision, the objects stick together, forming a combined mass (M).

• Combined mass (M): m₁ + m₂ = 1 kg + 5 kg = 6 kg

Using the definition of momentum (P = M × v_combined):

v_combined = P_after / M

v_combined = 10 kg·m·s⁻¹ / 6 kg

v_combined ≈ 1.67 m·s⁻¹

The velocity of the combined object is approximately 1.67 m·s⁻¹.

Q4. Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body.(5 Marks) 

Ans: 

Q5. Starting from a stationary position, Rahul paddles his bicycle to attain a velocity of 6 m s-1 in 30 s. Then he applies brakes such that the velocity of the bicycle comes down to 4 m s-1 in the next 5 s. Calculate the acceleration of the bicycle in both the cases.  (5 Marks) 

Ans: 

This problem is a direct calculation of acceleration in two phases, utilizing the formula derived from the rate of change of velocity. Acceleration (a) is defined as the change in velocity (v - u) divided by the time taken (t):

a = (v - u) / t

Case 1: Acceleration while Paddling

Rahul starts from a stationary position and accelerates uniformly.

Calculation:

a_{Case 1} = (6 m·s⁻¹ - 0 m·s⁻¹) / 30 s

a_{Case 1} = 0.2 m·s⁻²

The acceleration of the bicycle in the first case is 0.2 m·s⁻².

Case 2: Acceleration while Applying Brakes

The acceleration during braking is calculated using the velocity attained in the first case as the new initial velocity.

Calculation:

a_{Case 2} = (4 m·s⁻¹ - 6 m·s⁻¹) / 5 s

a_{Case 2} = -0.4 m·s⁻²

The acceleration of the bicycle in the second case is -0.4 m·s⁻². The negative sign indicates that the acceleration is opposite to the direction of motion, often called deceleration or retardation.