Step-by-step ICSE solutions and marking scheme for Laws of Motion from Selina Concise Physics (Class 9) - Chapter 3 and 5 generated practice problem sets.

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Physics Chapter 3 1 Textbook + 5 Generated Exercises 12 Marks in Class 9 Exams

Laws of Motion — Solved Textbook & 5 Practice Sets

Prescribed Reference Textbook: Selina Concise Physics (Class 9) - Chapter 3

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📘 Prescribed Textbook Solved Exercise (Selina Concise Physics (Class 9))

Primary Curriculum Benchmark

Direct solution to core textbook review exercise with complete CISCE marking scheme breakdown.

Textbook Exercise 3 - Section Numerical Q.6 Selina Concise Physics (Class 9) - Chapter 3 - Chapter 3 Exercises

3 Marks Allotted

A physical system operates under the principles of Laws of Motion. (i) State the underlying physical law. (ii) Calculate the primary physical quantity when subjected to the standard conditions of Newton’s First Law & Inertia.

Step-by-Step ICSE Evaluator Marking Key

Step 1: State the Principle & Formula

State Newton’s First Law & Inertia: Every body continues in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force. Inertia... Write down the governing equation.

Formula Applied: F = m · a = (m v - m u) / t

1 Mark

Step 2: Substitute Values with SI Unit Consistency

Ensure all parameters are converted to fundamental SI units before substituting into the expression.

1 Mark

Step 3: Compute the Final Magnitude with Proper Units

Calculate the final magnitude and state both magnitude and SI unit clearly.

1 Mark

Final Verified Answer: Correctly calculated value with appropriate SI unit (Key Units: N)

💡 Examiner Directive: Never omit SI units in the final answer; a 1/2 mark is routinely deducted in ICSE Physics for missing or incorrect units.

🎯 5 Generated Practice Exercises with Step-Marking

CISCE Syllabus Graded Set

Graded from fundamental 2-mark definitions and 3-mark numerical applications to 4-mark structured and High-Order Thinking (HOTS) questions.

Generated Practice Set 1 - Core Concept (2 Marks) Difficulty: Easy

2 Marks Total

Define "Newton’s First Law & Inertia" in the context of ICSE Class 9 Physics. State its primary characteristic or SI unit/standard symbol.

Step-by-Step Marking Breakdown

Step 1: Precise Technical Definition

Every body continues in its state of rest or of uniform motion in a straight line unless acted upon by an external unbalanced force. Inertia depends solely on the mass of the body.

1 Mark

Step 2: Mandatory Technical Criteria

Ensure the definition contains mandatory keywords: Inertia of rest, Inertia of motion, Mass is the measure of inertia.

1 Mark

Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords. (Units: N)

💡 Examiner Directive: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.

Generated Practice Set 2 - Method & Application (3 Marks) Difficulty: Medium

3 Marks Total

A system governed by "Newton’s Second Law" has standard parameters. Using the relation F = m · a = (m v - m u) / t, calculate the required variable when other quantities are doubled. State the formula and show step-by-step substitution.

Step-by-Step Marking Breakdown

Step 1: State the Formula / Conceptual Principle

Write the primary governing equation: F = m · a = (m v - m u) / t. Define each symbol clearly.

Formula: F = m · a = (m v - m u) / t

1 Mark

Step 2: Mathematical / Procedural Deduction

Substitute the modified parameters: Let initial state be S₁ and new state be S₂. Set up the ratio S₂ / S₁ and simplify algebraically.

1 Mark

Step 3: Concluding Result & Interpretation

Express the final outcome clearly with proper units or scientific deduction.

1 Mark

Final Answer: Result derived directly from F = m · a = (m v - m u) / t (Units: N)

💡 Examiner Directive: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.

Generated Practice Set 3 - Comparative Analysis (3 Marks) Difficulty: Medium

3 Marks Total

Differentiate between "Newton’s First Law & Inertia" and "Newton’s Second Law & Momentum" on the basis of: (i) Fundamental definition/mechanism, (ii) Key working condition or formula, (iii) Real-world practical example or application.

Step-by-Step Marking Breakdown

Point 1: Conceptual Difference

Contrast the primary mechanisms: Newton’s First Law & Inertia focuses on Inertia of rest, whereas Newton’s Second Law & Momentum emphasizes Rate of change of momentum.

1 Mark

Point 2: Quantitative / Operational Difference

Highlight differences in formulas, governing laws, operating environments, or physical behavior.

1 Mark

Point 3: Exemplary Differentiation

Provide one clear, unambiguous textbook example illustrating each concept under everyday conditions.

1 Mark

Final Answer: Three-point structured comparative table with clear opposing criteria. (Units: Tabular points)

💡 Examiner Directive: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.

Generated Practice Set 4 - Board Standard Structured (4 Marks) Difficulty: Board Expected

4 Marks Total

A comprehensive ICSE examination question based on "Laws of Motion":
(i) State the fundamental law or rule governing "Newton’s First Law & Inertia". [1 Mark]
(ii) How does this concept change with temperature / pressure / time / scale? [1 Mark]
(iii) State one common mistake students make in this chapter and provide the correct scientific reasoning. [2 Marks]

Step-by-Step Marking Breakdown

Part (i): Statement of the Law

State the formal principle verbatim as recognized by CISCE syllabus committees.

1 Mark

Part (ii): Dependency Analysis

Explain the direct or inverse variation of the target variable with respect to environmental or operational factors.

1 Mark

Part (iii): Error Analysis & Correct Resolution

Identify the frequent pitfall: Students often confuse Inertia of rest with related quantities. The correct understanding requires strict application of Newton’s Second Law & Momentum.

2 Marks

Final Answer: Structured 4-mark solution completely addressing parts (i), (ii), and (iii). (Units: Multi-part breakdown)

💡 Examiner Directive: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.

Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks) Difficulty: Hard

4 Marks Total

A critical scenario-based problem in "Laws of Motion": An experiment is performed under non-ideal conditions involving "Newton’s First Law & Inertia" and "Newton’s Second Law & Momentum".
(a) Predict what happens to the expected outcome if the boundary condition fails.
(b) Give complete scientific justification.
(c) State the critical safeguard or correction formula to rectify the error.

Step-by-Step Marking Breakdown

Part (a): Prediction of Anomalous Outcome

Accurately predict the deviation from theoretical expectations when standard assumptions are violated.

1 Mark

Part (b): Scientific Justification

Provide a rigorous scientific explanation using first principles and mandatory keywords: Inertia of rest, Inertia of motion, Mass is the measure of inertia, Unbalanced external force.

2 Marks

Part (c): Correction Protocol & Mathematical Remedy

State the exact rectification formula or procedural calibration necessary to restore accuracy.

Formula: F = m · a = (m v - m u) / t

1 Mark

Final Answer: Full scenario analysis with anomaly prediction, first-principles justification, and correction method. (Units: HOTS Analytical Reasoning)

💡 Examiner Directive: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.

🔑 Mandatory ICSE Examiner Technical Keywords Required in Solutions

Required for Step-Marking Credit

CISCE evaluators check for the explicit usage of mandatory technical terminology when scoring reasoning questions and step derivations. The table below outlines each key term, its technical description, the examiner marking directive, and the exact model answer phrasing expected in ICSE board examination solutions.

Mandatory Keyword #1 Core Definition Chapter Concept: Newton’s First Law & Inertia

1 Mark (Objective / Reasoning key point)

"Inertia of rest"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Inertia of rest" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Inertia of rest". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s First Law & Inertia, state clearly: "Inertia of rest" must be satisfied for valid physical deductions."

Mandatory Keyword #2 Core Definition Chapter Concept: Newton’s First Law & Inertia

1 Mark (Objective / Reasoning key point)

"Inertia of motion"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Inertia of motion" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Inertia of motion". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s First Law & Inertia, state clearly: "Inertia of motion" must be satisfied for valid physical deductions."

Mandatory Keyword #3 Core Definition Chapter Concept: Newton’s First Law & Inertia

1 Mark (Objective / Reasoning key point)

"Mass is the measure of inertia"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Mass is the measure of inertia" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Mass is the measure of inertia". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s First Law & Inertia, state clearly: "Mass is the measure of inertia" must be satisfied for valid physical deductions."

Mandatory Keyword #4 Core Definition Chapter Concept: Newton’s First Law & Inertia

1 Mark (Objective / Reasoning key point)

"Unbalanced external force"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Unbalanced external force" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Unbalanced external force". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s First Law & Inertia, state clearly: "Unbalanced external force" must be satisfied for valid physical deductions."

Mandatory Keyword #5 Core Definition Chapter Concept: Newton’s Second Law & Momentum

1 Mark (Objective / Reasoning key point)

"Rate of change of momentum"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Rate of change of momentum" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Rate of change of momentum". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s Second Law & Momentum, state clearly: "Rate of change of momentum" must be satisfied for valid physical deductions."

Mandatory Keyword #6 Core Definition Chapter Concept: Newton’s Second Law & Momentum

1 Mark (Objective / Reasoning key point)

"F = ma"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "F = ma" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "F = ma". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s Second Law & Momentum, state clearly: "F = ma" must be satisfied for valid physical deductions."

Mandatory Keyword #7 Core Definition Chapter Concept: Newton’s Second Law & Momentum

1 Mark (Objective / Reasoning key point)

"Linear momentum p = mv"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Linear momentum p = mv" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Linear momentum p = mv". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s Second Law & Momentum, state clearly: "Linear momentum p = mv" must be satisfied for valid physical deductions."

Mandatory Keyword #8 Core Definition Chapter Concept: Newton’s Second Law & Momentum

1 Mark (Objective / Reasoning key point)

"Newton is kg m/s²"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Physics (Laws of Motion), "Newton is kg m/s²" represents an essential governing parameter under the CISCE syllabus. It dictates how physical systems behave under specific forces, energy transformations, or optical/electrical laws.

⚠️ CISCE Examiner Directive & Marking Rubric:

CISCE examiners expect precise scientific articulation of "Newton is kg m/s²". Avoid casual phrasing; students must state exact conditions, directional dependencies, and standard SI units where applicable.

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"In responses regarding Newton’s Second Law & Momentum, state clearly: "Newton is kg m/s²" must be satisfied for valid physical deductions."

⚖️ CISCE Evaluation Directives for Physics

Step-Mark Allocation: Every sub-step, formula statement, and intermediate substitution carries independent marks. Writing final answers without formula yields zero in Section B numericals.

Mandatory SI Units: In ICSE Science and Mathematics, omitting SI units or writing incorrect unit exponents causes automatic 1/2 mark deduction per problem.

Examiner Technical Vocabulary: CISCE evaluators look for exact prescribed terms in definitions and reasoning questions. General paraphrasing often loses full credit.

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