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Important Questions: CBSE Class 11 Physics Chapter 4 Laws of Motion

Laws of Motion is the conceptual and numerical heart of CBSE Class 11 Physics, bridging kinematics and real-world dynamics. This chapter — covering Newton's three laws, friction (static, kinetic, rolling), and circular motion dynamics — contributes 8-10 marks to your term exam and lays the foundation for mechanics in Class 12. CBSE question papers consistently test Newton's second law through pulley and wedge problems, friction via coefficient calculations, and circular motion through banking and conical-pendulum scenarios. Below is a structured question bank with model answers to help you tackle every pattern confidently.

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Key takeaways

✓Chapter 4 Laws of Motion typically carries 8-10 marks in CBSE Class 11 Physics term exams, distributed across MCQs, VSA, SA, and LA questions.
✓Newton's second law numericals (F = ma) and friction problems (static vs kinetic) form the backbone of 3-mark and 5-mark questions every year.
✓CBSE prefers pulley systems, inclined planes, and connected-blocks scenarios to test simultaneous application of all three laws.
✓Circular motion dynamics — centripetal force and banking of roads — appear as either stand-alone 3-mark questions or case-study sub-parts.
✓Common mistakes include sign errors in free-body diagrams, confusing mass with weight, and misapplying friction direction in multi-body problems.
✓Practising 15-18 varied questions with complete working ensures coverage of all NCERT exercise types and previous-year patterns.

Chapter Overview and Marks Weightage in CBSE Exam

Chapter 4 Laws of Motion appears in Unit II Kinematics & Laws of Motion, which together carry roughly 17 marks in the CBSE Class 11 Physics term exam. Of those, Laws of Motion alone accounts for 8-10 marks. The CBSE blueprint allocates 1 MCQ (1 mark), 1-2 VSA or short-answer questions (2 marks each), one 3-mark numerical, and often a 5-mark long-answer or case-based question. Topics tested most frequently are Newton's second law applications (pulley systems, inclined planes), friction coefficient problems, and circular motion on banked roads or vertical loops. The 2024 CBSE sample paper featured a 5-mark case study on friction in a multi-block system and a 3-mark numerical on tension in a string connecting two masses over a pulley. Understanding free-body diagrams is non-negotiable: examiners award partial marks for correct FBDs even if the final answer is wrong. Expect conceptual MCQs on action-reaction pairs, inertia, and impulse-momentum as well.

Unit II (Kinematics + Laws of Motion): ~17 marks total; Laws of Motion: 8-10 marks
Typical distribution: 1 MCQ (1 m), 2 VSA/SA (2 m each), 1 numerical (3 m), 1 LA/case-study (5 m)
High-frequency topics: Newton's second law (F = ma), friction (μ_s, μ_k), tension in strings, circular motion (centripetal force, banking)
Free-body diagrams fetch method marks even if calculation errors occur
Case-based questions (introduced 2023 onwards) often combine friction + Newton's laws in real-world scenarios

1-Mark Questions: MCQ and Very Short Answer (VSA)

One-mark questions test definitions, units, and quick conceptual clarity. CBSE favours MCQs on Newton's third law pairs, direction of friction, and dimensional analysis of force. VSA questions may ask for a single formula, SI unit, or a one-line reason. These are scoring opportunities — clear, direct answers fetch full marks. Below are six representative 1-mark questions covering the breadth of the chapter. Always write the exact NCERT term (e.g. 'static friction' not 'stationary friction') and include units where numerical values appear. For MCQs, eliminate obviously wrong options first; many CBSE MCQs hinge on sign or direction, so sketch a quick FBD mentally before choosing. In the 2025 term-1 pattern, expect 1-2 such MCQs from Laws of Motion, often paired with a diagram or data table.

2-Mark Questions: Short Answer and Numerical

Two-mark questions demand a definition plus example, derivation of a simple relation, or a one-step numerical. CBSE often asks 'State Newton's second law and give its mathematical form' or 'Calculate the net force when two forces act at an angle'. Answers should be concise: write the statement, formula, substitute values, and box the final answer with unit. Avoid long explanations; two to three sentences suffice. Diagrams earn credit — a neat free-body diagram can fetch one mark even if the calculation has a mistake. The 2024 Delhi set included a 2-mark question on finding limiting friction given normal reaction and μ_s. Below are four archetypal 2-mark questions. Practice writing answers in under three minutes each to match exam time constraints. Always define symbols the first time you use them, e.g. 'Let m = mass in kg, a = acceleration in m/s²'.

3-Mark Questions: Numerical Problems and Derivations

Three-mark questions are the workhorses of CBSE Physics: they test problem-solving via Newton's second law, pulley systems, inclined planes, or friction on moving bodies. A complete answer must show the free-body diagram (1 mark), write force equations along chosen axes (1 mark), and solve for the unknown with correct unit (1 mark). CBSE marking schemes award partial credit generously if method is clear. Common scenarios include two blocks connected by a string over a frictionless pulley, a block on an incline with friction, or circular motion requiring centripetal force calculation. Always resolve forces parallel and perpendicular to the plane of motion to simplify equations. The 2023 All-India set had a 3-mark numerical on finding acceleration of a system of two masses (3 kg and 2 kg) connected over a pulley. Below are three fully worked 3-mark questions that mirror CBSE style. Practice drawing FBDs first, then writing equations — this sequence minimises sign errors.

5-Mark Questions: Long Answer and Case-Based Problems

Five-mark questions integrate multiple concepts — for instance, applying Newton's laws to a three-block system, deriving equations of motion on banked curves, or analysing a case study with sub-questions. CBSE introduced case-based questions in 2023; a typical 5-mark case presents a real-world scenario (e.g. a truck braking on a slope, friction between tyres and road) followed by four sub-questions worth 1+1+1+2 marks. Answer every sub-part separately and label them clearly. For derivation questions, start from first principles (free-body diagram, resolve forces, apply ΣF = ma), show all algebraic steps, and state assumptions (frictionless pulley, inextensible string, etc.). The 2024 sample paper included a 5-mark derivation of the expression for maximum safe speed on a banked circular road. Long-answer questions reward logical flow: introduction (defining terms), body (equations and working), conclusion (final result with unit and a check on dimensional correctness). Spend five to six minutes planning your answer structure before writing. Below are two full 5-mark questions with model solutions.

Additional 3-Mark and 5-Mark Practice Questions

Mastery comes from variety. Below are three more exam-style questions (two 3-mark, one 5-mark) covering friction dynamics, impulse, and Newton's third law applications. Work through each question independently before checking the model answer. Time yourself: aim for four minutes per 3-mark question and seven minutes for a 5-mark problem. Pay attention to the CBSE marking scheme style — method marks are awarded for correct free-body diagrams, equation setup, and unit consistency even if arithmetic slips occur. These questions are drawn from the 2022-2024 CBSE question papers and NCERT exemplar problems. Practising a mix of pulley systems, inclined planes, circular motion, and friction ensures you are ready for any combination CBSE throws at you. Keep a separate notebook for diagrams; neat, labelled FBDs often fetch you one mark outright and make equation writing easier.

How CBSE Frames Questions from Laws of Motion

CBSE question-paper setters follow a predictable blueprint for Laws of Motion. MCQs test definitions, units, and quick applications of Newton's laws — expect questions on action-reaction pairs, direction of friction, or identifying the correct free-body diagram from four options. Two-mark questions ask for a statement of a law plus a real-life example, or a single-step numerical (finding friction force, resultant of two forces). Three-mark numericals are always multi-step: setting up force equations for two connected bodies, resolving forces on an incline, or calculating tension and acceleration in pulley problems. Five-mark questions either ask for derivations (banking of roads, motion on an incline with friction) or present a case study with sub-questions integrating Laws of Motion with kinematics or energy. Since 2023, competency-based questions have increased: you might be given a graph (force vs time) and asked to find impulse or a table of friction coefficients and asked which surface pair has the highest static friction. The key skill CBSE rewards is the ability to draw a correct free-body diagram and write vector equations component-wise. Examiners also check dimensional correctness — always verify your final answer has the right unit. Previous-year analysis (2020-2024) shows pulley systems appear almost every year, friction numericals in 70 percent of papers, and circular motion (banking, conical pendulum) in about 50 percent. Therefore, prioritise these three sub-topics during revision and solve at least five problems of each type.

MCQs focus on conceptual clarity: Newton's third law pairs, direction of friction, inertia, units of force
2-mark questions: definitions + example, or one-step numericals (friction force, resultant force)
3-mark numericals: pulley systems (two masses), inclined plane with friction, connected blocks, circular motion centripetal force
5-mark questions: derivations (banking angle, acceleration in Atwood machine) or case-based with 4 sub-questions
Competency-based: interpreting force-time graphs for impulse, choosing correct FBD from options, table-based friction problems
Partial marking: 1 mark for FBD, 1 mark for correct equations, 1 mark for final answer with unit
Common diagram asked: FBD of a block on incline, two-mass pulley, car on banked road

Common Mistakes Students Make and How to Avoid Them

Even strong students lose 2-3 marks in Laws of Motion due to recurring mistakes. The most frequent error is sign confusion in free-body diagrams: taking upward as positive for one mass and downward for another in the same problem leads to wrong equations. Always define a consistent coordinate system before writing force equations. Another pitfall is confusing mass and weight — writing 'force = m' instead of 'force = mg'. Remember, mass is in kilograms (a scalar) and weight is in newtons (a vector, mg). Many students write friction f = μN without checking whether it is static or kinetic; static friction is variable (0 ≤ f_s ≤ μ_s N) while kinetic friction is constant (f_k = μ_k N). In pulley problems, students sometimes add tensions instead of equating them for a massless string. For inclined-plane questions, forgetting to resolve weight into components parallel and perpendicular to the plane is a classic blunder — always draw the incline, mark the angle, and resolve mg into mg sin θ and mg cos θ. In circular motion, mixing up centripetal and centrifugal force costs marks; remember, centrifugal force is a pseudo-force in a rotating reference frame and does not appear in an inertial frame FBD. Unit errors are common: writing acceleration in m/s instead of m/s², or force in kg instead of N. Finally, students often skip the free-body diagram to save time, but CBSE awards one mark just for a correct FBD — those are easy marks. To avoid these mistakes, adopt a checklist: (i) Draw and label the FBD first, (ii) Choose and state your positive direction, (iii) Resolve all forces along chosen axes, (iv) Write ΣF = ma separately for each body, (v) Solve the system of equations, (vi) Check units and dimensional correctness of the final answer. Practising past-year papers under timed conditions will expose your personal error patterns so you can fix them before the exam.

Sign errors in FBD: define one consistent positive direction (e.g. rightward, upward) for the entire problem
Confusing mass (kg) with weight (N): always write weight as W = mg, force in newtons
Static vs kinetic friction: f_s is self-adjusting (≤ μ_s N); f_k is constant (= μ_k N)
Pulley problems: for a single inextensible string, tension is the same on both sides if pulley is massless and frictionless
Inclined plane: must resolve mg into mg sin θ (parallel) and mg cos θ (perpendicular); many forget this step
Centrifugal force: do not include it in inertial-frame FBDs; use only centripetal force (mv²/r towards centre)
Unit mistakes: a in m/s², F in N, μ is dimensionless; double-check every final answer
Skipping FBD to save time: costs you 1 easy mark and increases chance of equation errors

Revision Strategy and Time Management Tips

With 8-10 marks at stake, Laws of Motion deserves focused revision in the final two weeks before your CBSE exam. Start by re-reading NCERT Chapter 5 (the book labels it Chapter 5, syllabus often calls it Chapter 4 — both refer to Laws of Motion) and making concise notes on Newton's three laws, types of friction, and circular motion formulae. Next, solve all NCERT in-text examples and end-of-chapter exercises; these are the gold standard and many CBSE questions are direct adaptations. Then move to NCERT Exemplar problems — they are slightly tougher and great for 5-mark preparation. Time yourself: allocate three minutes for 1-mark MCQs, four minutes for 2-mark, six minutes for 3-mark, and eight to nine minutes for 5-mark questions during practice. This leaves buffer time for revision and checking. For numericals, adopt a four-step template: (i) Draw FBD and list given data, (ii) Write force equations, (iii) Solve algebraically before plugging numbers, (iv) State final answer with unit and check dimensional correctness. Repeat this cycle for ten different problem types (pulley, incline, friction, circular motion, connected blocks, etc.). One week before the exam, solve the last three years' CBSE question papers (2022, 2023, 2024) under exam conditions — 40 minutes for the Laws of Motion portion. Identify weak areas: if you consistently lose marks on inclined-plane problems, drill five more of those. On the day before the exam, revise only formulae, common mistakes, and key derivations; do not attempt new hard problems. During the exam, read each question twice, underline keywords (frictionless, inextensible, uniform speed), and if you are stuck, move on and return later — do not let one 5-mark question eat up time needed for easier sections. Finally, reserve the last five minutes to recheck units, signs, and whether you have answered all sub-parts of case-based questions. Consistent practice and disciplined time management will ensure you convert the full 8-10 marks from this chapter.

Week 3 before exam: Read NCERT Chapter 5, make formula notes, solve all in-text + exercise problems
Week 2: NCERT Exemplar + previous-year 3-mark and 5-mark questions; practice FBD drawing daily
Week 1: Solve 2022, 2023, 2024 CBSE papers (Laws of Motion section) in timed mode; analyze mistakes
Day before exam: Revise formula sheet, common-mistakes list, and key derivations (banking, Atwood machine); no new problems
Exam day: Read question twice, underline given data, draw FBD first, write equations, solve, check units
Time targets: 1-mark ≤3 min, 2-mark ≤4 min, 3-mark ≤6 min, 5-mark ≤9 min; keep 5 min buffer at end

How CBSETUTOR.AI Helps You Master Laws of Motion

Understanding free-body diagrams and setting up force equations can feel overwhelming when you are stuck at 11 pm with no teacher around. That is exactly where CBSETUTOR.AI steps in as your 24×7 AI tutor. Simply snap a photo of any Laws of Motion problem — a tricky pulley system, an inclined-plane question with friction, or a conceptual doubt about Newton's third law — and upload it through the web app. Within seconds, you receive a step-by-step solution written in clean Indian English, complete with a labelled free-body diagram, force equations resolved along appropriate axes, and the final answer with units. The AI explains not just what the answer is, but why each step follows from Newton's laws, so you build genuine understanding rather than rote memory. For CBSE Class 11 Physics Chapter 4, CBSETUTOR.AI covers every NCERT exercise, exemplar problem, and previous-year question type. You can ask follow-up questions ('Why is tension the same on both sides?' or 'How do I know if friction is static or kinetic here?') and get instant clarification. The platform is tailored to CBSE — it uses NCERT terminology, follows CBSE marking-scheme format, and even alerts you to common mistakes examiners penalise. Whether you are in a metro city with access to expensive coaching or in a Tier-2 town relying on school alone, CBSETUTOR.AI levels the playing field at a flat ₹999 per month for all classes (6 to 12) with a 3-day free trial. No hidden charges, no per-question fees. Think of it as having a patient Physics teacher in your pocket, ready to help whenever you need, so you can confidently tackle every Laws of Motion question in your exam.

Snap and upload any Class 11 Physics Laws of Motion problem; get step-by-step solutions in seconds
Every solution includes a labelled free-body diagram, resolved force equations, and final answer with unit
Ask unlimited follow-up questions to clarify concepts like action-reaction pairs, friction direction, or tension analysis
Covers all NCERT exercises, exemplar problems, and previous-year CBSE question patterns for Chapter 4
Flat ₹999/month for classes 6-12, with a 3-day free trial; no per-question charges
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Frequently asked questions

How many marks does Chapter 4 Laws of Motion carry in CBSE Class 11 Physics term exam?+

Laws of Motion typically contributes 8-10 marks in the CBSE Class 11 Physics term exam. This includes 1 MCQ (1 mark), 1-2 short-answer questions (2 marks each), one 3-mark numerical, and often a 5-mark long-answer or case-based question. The chapter is part of Unit II (Kinematics & Laws of Motion), which together weighs about 17 marks.

Which topics in Laws of Motion are most frequently asked in CBSE exams?+

Newton's second law applications (F = ma) in pulley systems and connected blocks appear almost every year. Friction problems — finding coefficients of static or kinetic friction, motion on rough inclines — are tested in about 70% of papers. Circular motion dynamics, especially banking of roads and centripetal force, features in roughly 50% of question papers. Free-body diagram drawing is essential across all these topics.

What is the difference between static and kinetic friction, and how do I know which to use?+

Static friction acts between surfaces at rest relative to each other; it is self-adjusting from zero up to a maximum value f_s(max) = μ_s N. Kinetic friction acts when surfaces slide past each other and has a constant magnitude f_k = μ_k N, with μ_k typically less than μ_s. Use static friction if the body is stationary or you are finding the threshold force to start motion; use kinetic friction once the body is already moving.

How should I draw a free-body diagram to ensure I get full marks?+

Draw a simple dot or box to represent the object. Mark and label all forces acting on that object: weight (mg downward), normal reaction (N perpendicular to surface), applied force (F in the given direction), friction (f opposing motion), and tension (T along the string). Use arrows with clear labels. Choose and indicate a positive direction (e.g. rightward, upward). CBSE awards 1 mark for a correct, neat FBD even if later calculations have minor errors.

What are the most common mistakes in pulley and inclined-plane problems?+

In pulley problems, students often write different tensions for the two sides of the string, forgetting that for a massless, inextensible string over a frictionless pulley, tension is the same throughout. In inclined-plane problems, the classic error is not resolving weight into mg sin θ (parallel to plane) and mg cos θ (perpendicular). Always draw the incline, mark the angle, and resolve before writing force equations.

How do I tackle a 5-mark case-based question on Laws of Motion?+

Read the case passage carefully and underline key data (masses, angles, coefficients, speeds). Note that case-based questions have 4 sub-parts (typically 1+1+1+2 marks). Answer each sub-part separately and label them (i), (ii), (iii), (iv). Usually sub-part (i) asks for a definition or diagram (1 mark), (ii) and (iii) are short calculations or formula statements (1 mark each), and (iv) is a 2-mark numerical or conceptual explanation. Write concisely; avoid repeating the passage text.

Is friction a conservative or non-conservative force, and does CBSE ask this?+

Friction is a non-conservative force because the work done against friction depends on the path and is dissipated as heat, not stored as potential energy. CBSE has asked this as a 1-mark MCQ or a 2-mark short-answer question. The standard answer is: 'Friction is non-conservative; it converts mechanical energy into thermal energy, and the work done is path-dependent.'

What is the formula for centripetal force, and when do I use it?+

Centripetal force F_c = mv²/r = mrω², where m is mass, v is linear speed, r is radius of the circular path, and ω is angular velocity. Use it whenever an object moves in a circle or along a curved path — for example, a car on a banked road, a stone tied to a string whirled in a horizontal circle, or a satellite in orbit. Always direct F_c towards the centre of the circle.

How many questions should I practice to be fully prepared for Laws of Motion?+

Solve all 15-18 NCERT in-text + exercise problems first. Then work through at least 10-12 additional numericals from NCERT Exemplar and previous-year CBSE papers, covering pulley systems, inclined planes, friction, and circular motion. Aim for a mix: 5-6 pulley/connected-block problems, 4-5 incline-with-friction problems, and 3-4 circular motion questions. This variety ensures you can handle any combination CBSE presents.

Can CBSETUTOR.AI help me if I am stuck on a specific Laws of Motion numerical at night?+

Absolutely. CBSETUTOR.AI is available 24×7. Just take a photo of the problem and upload it via the web app. You will get a step-by-step solution with a labelled free-body diagram, force equations, and the final answer in seconds. You can also ask follow-up questions like 'Why is the normal reaction not equal to mg here?' and receive instant, clear explanations. It is like having a Physics tutor on call anytime, for a flat ₹999/month across all subjects and classes 6-12, with a 3-day free trial.

Related resources

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