Class 9 Science Chapter 9 Friction MCQ with Answers | Complete CBSE Quiz

The revised CBSE Class 9 Science syllabus has shifted towards competency-based assessment, where multiple-choice questions test deeper understanding rather than rote memorization. MCQs force you to think critically: you must eliminate wrong options, spot subtle distinctions (e.g., between static and kinetic friction), and apply concepts to unfamiliar scenarios. In the new pattern, roughly 40–50% of marks come from objective questions. Friction—a chapter on forces and motion—appears in multiple MCQ formats: direct recall ("What is static friction?"), numerical reasoning (calculating friction force using f = μN), and assertion-reason pairs ("Assertion: Friction increases with surface roughness. Reason: Friction depends only on normal force."). Practising varied MCQ types trains your brain to recognize question traps, manage exam stress, and maximize marks in minimal time. Unlike long-answer questions, MCQs deliver instant feedback, helping you identify weak spots immediately.

**Question 1:** Friction is a force that: A) Always opposes motion B) Acts only when objects are moving C) Always acts parallel to the surface of contact D) Acts perpendicular to the normal force **Answer: C** | **Reason:** Friction always acts parallel (tangent) to the contact surface, opposing the direction of motion or tendency to move. **Question 2:** Static friction is: A) Friction when an object is moving B) Friction that prevents an object from moving C) Friction that depends only on weight D) Friction that is always greater than kinetic friction **Answer: B** | **Reason:** Static friction acts on stationary objects and prevents them from sliding until applied force exceeds maximum static friction. **Question 3:** Kinetic friction occurs when: A) An object is about to move B) An object is already sliding on a surface C) An object is resting on a table D) Applied force equals friction force **Answer: B** | **Reason:** Kinetic friction acts on moving objects; it opposes their motion and is usually smaller than maximum static friction. **Question 4:** The coefficient of friction (μ) is: A) Measured in Newtons B) A dimensionless quantity C) The same for all pairs of surfaces D) Always equal to 1 **Answer: B** | **Reason:** Coefficient of friction is a ratio (f/N) with no units; it varies with material pairs and surface conditions. **Question 5:** Normal force is: A) The force applied horizontally on an object B) The gravitational force acting downward C) The perpendicular force exerted by a surface on an object D) The force opposing motion **Answer: C** | **Reason:** Normal force (N) is perpendicular to the contact surface; on a horizontal plane, N = mg (weight). **Question 6:** Friction force is calculated using: A) f = m × a B) f = μN C) f = mg D) f = v²/r **Answer: B** | **Reason:** The friction force formula is f = μN, where μ is the coefficient of friction and N is the normal force. **Question 7:** Which type of friction is the largest? A) Rolling friction B) Fluid friction C) Static friction D) Kinetic friction **Answer: C** | **Reason:** Maximum static friction is typically larger than kinetic friction for the same pair of surfaces, allowing objects to start moving when the applied force exceeds static friction. **Question 8:** Friction depends on: A) Weight and velocity B) Surface area and speed C) Nature of surfaces and normal force D) Shape and colour of objects **Answer: C** | **Reason:** Friction depends on the coefficient of friction (determined by material types) and normal force; it is independent of surface area or speed. **Question 9:** Rolling friction is: A) Friction between a rolling wheel and the ground B) Friction in fluids C) Friction that acts on stationary objects D) Friction greater than kinetic friction **Answer: A** | **Reason:** Rolling friction acts on a wheel or sphere rolling on a surface; it is much smaller than sliding kinetic friction. **Question 10:** Fluid friction acts on objects moving through: A) Air only B) Water only C) Gases and liquids D) Solid surfaces **Answer: C** | **Reason:** Fluid friction (drag) acts on objects moving through any fluid—gases (air) or liquids (water, oil)—and increases with speed and surface area.

**Question 11:** A block of mass 5 kg rests on a horizontal surface. If the coefficient of static friction is 0.4 and g = 10 m/s², what is the maximum static friction force? A) 10 N B) 15 N C) 20 N D) 25 N **Answer: C** | **Reason:** Maximum static friction = μₛ × N = 0.4 × (5 × 10) = 0.4 × 50 = 20 N. **Question 12:** A box is pushed with a force of 30 N on a horizontal surface. The friction force is 20 N. The net force on the box is: A) 10 N B) 20 N C) 30 N D) 50 N **Answer: A** | **Reason:** Net force = Applied force − Friction force = 30 − 20 = 10 N (in the direction of applied force). **Question 13:** Which statement is true about friction on an inclined plane? A) Normal force equals weight B) Normal force equals mg cos θ C) Friction does not depend on the angle of inclination D) Kinetic friction equals weight **Answer: B** | **Reason:** On an inclined plane, the normal force N = mg cos θ (perpendicular component of weight); friction f = μN = μmg cos θ. **Question 14:** A car tyre experiences greater friction than a block sliding on ice because: A) Tyres are heavier B) Tyres have higher coefficient of friction and better surface contact C) Ice is a liquid D) Friction is independent of surface texture **Answer: B** | **Reason:** Tyre rubber has a high coefficient of friction (μ ≈ 0.7–1.0), and treads increase contact; ice has low μ (≈ 0.02–0.05). **Question 15:** If the coefficient of kinetic friction between a 2 kg block and a table is 0.25, the kinetic friction force is (g = 10 m/s²): A) 2.5 N B) 5 N C) 10 N D) 20 N **Answer: B** | **Reason:** f = μₖN = 0.25 × (2 × 10) = 0.25 × 20 = 5 N. **Question 16:** Why does a bicycle move forward when you pedal? A) There is no friction between the tyre and ground B) Friction between the tyre and ground acts backward C) Friction between the tyre and ground acts forward, propelling the bike D) Friction only acts on the pedals **Answer: C** | **Reason:** The tyre pushes the ground backward; by Newton's third law, the ground exerts a forward friction force on the tyre, moving the bike forward. **Question 17:** Lubricants reduce friction because they: A) Increase the coefficient of friction B) Create a fluid layer between surfaces, replacing solid-to-solid contact C) Increase the normal force D) Reduce the weight of objects **Answer: B** | **Reason:** Lubricants form a thin liquid film between surfaces, changing friction from solid friction (μ ≈ 0.2–1.0) to fluid friction (much lower). **Question 18:** A ball rolling on grass experiences rolling friction. This friction is: A) Equal to kinetic friction on the same surface B) Usually much smaller than kinetic friction C) Independent of the ball's radius D) Greater than static friction **Answer: B** | **Reason:** Rolling friction is typically 100–1000 times smaller than kinetic friction because the contact point moves instantaneously (no sliding). **Question 19:** Two identical wooden blocks are tested: one on dry concrete, another on wet concrete. Which experiences greater friction? A) Dry concrete B) Wet concrete C) Both have equal friction D) Cannot be determined **Answer: A** | **Reason:** Dry concrete has a higher coefficient of friction (μ ≈ 0.5–0.7) than wet concrete (μ ≈ 0.3–0.5), so dry surface provides more friction. **Question 20:** A sports car has treaded tyres instead of smooth ones to: A) Reduce weight B) Increase grip and friction with the road C) Decrease normal force D) Reduce fuel consumption **Answer: B** | **Reason:** Treads increase the effective contact area and create interlocking with the road surface, significantly increasing the coefficient of friction.

**Question 21:** **Assertion:** Friction is always harmful and should be eliminated. **Reason:** Friction opposes motion and wastes energy. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: D** | **Reason:** Friction is essential for walking, writing, and vehicle control; the assertion is false because friction has many beneficial roles, even though the reason is true. **Question 22:** **Assertion:** The coefficient of static friction is always greater than or equal to the coefficient of kinetic friction. **Reason:** It takes more force to start moving an object than to keep it moving. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** μₛ ≥ μₖ because more force is needed to overcome static friction (initial resistance); the reason correctly explains the assertion. **Question 23:** **Assertion:** Friction force is independent of the surface area in contact. **Reason:** Friction depends on the normal force and coefficient of friction, not on how the weight is distributed. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** f = μN; since N is perpendicular force (not total contact area), friction is independent of surface area; the reason fully explains this. **Question 24:** **Assertion:** A book sliding across a table experiences kinetic friction that increases if you push it faster. **Reason:** Kinetic friction increases with the velocity of the object. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: C** | **Reason:** Kinetic friction (f = μₖN) is independent of velocity; the assertion is false because faster motion does not increase kinetic friction. **Question 25:** **Assertion:** Fluid friction increases with the speed of an object moving through a fluid. **Reason:** Drag force depends on velocity, surface area, and the density of the fluid. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: B** | **Reason:** Both are true, but the reason lists factors without directly explaining why speed increases drag; the reason is not a complete causal explanation. **Question 26:** **Assertion:** A car on a wet road has a longer stopping distance than on a dry road. **Reason:** Wet roads reduce the coefficient of friction between tyres and the road. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** On wet roads, μ decreases (water acts as a lubricant), so friction force (f = μN) decreases, requiring longer braking distance; the reason correctly explains the assertion. **Question 27:** **Assertion:** Rolling friction is less than kinetic friction for the same object on the same surface. **Reason:** In rolling motion, the contact point is instantaneously at rest, eliminating sliding friction. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** Rolling objects deform slightly at contact; this deformation reduces friction compared to sliding; the reason correctly explains why rolling friction is smaller. **Question 28:** **Assertion:** Oil applied between two sliding surfaces reduces friction but does not change the normal force. **Reason:** Lubricants work by reducing the coefficient of friction, not by changing the applied load. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** Lubricants reduce μ (f = μN); since N remains unchanged, friction decreases only through a lower μ; the reason correctly explains the assertion. **Question 29:** **Assertion:** A block at rest on a ramp will not slide if the applied force (down the slope) is less than the maximum static friction. **Reason:** Maximum static friction = μₛ × mg cos θ. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** The block remains at rest as long as applied force ≤ fₛ,ₘₐₓ = μₛN = μₛ mg cos θ; the reason correctly gives the formula for maximum static friction on a ramp. **Question 30:** **Assertion:** Snowboarders wax their boards to reduce friction and increase speed. **Reason:** Wax lowers the coefficient of friction between the board and snow. A) Both A and R are true, R is the correct explanation of A B) Both A and R are true, R is NOT the correct explanation of A C) A is true, R is false D) A is false, R is true **Answer: A** | **Reason:** Wax creates a smooth, low-friction surface (μ decreases); lower friction (f = μN) allows faster motion; the reason correctly explains the assertion.

**Trap 1: Confusing Normal Force with Weight** — Many students choose answers assuming N = mg on an inclined plane, forgetting that N = mg cos θ. On a slope, gravity has two components: perpendicular (N) and parallel (mg sin θ). Always draw a free-body diagram before calculating friction. **Trap 2: Thinking Friction Depends on Surface Area** — The formula f = μN proves friction is independent of contact area. A block placed flat or on its edge experiences the same friction (same N and μ). This trap catches many students because intuition suggests more surface = more friction, but experimental data contradicts this. **Trap 3: Assuming Kinetic Friction Increases with Speed** — Kinetic friction is constant for a given pair of surfaces (f = μₖN) and does NOT depend on velocity. Students often confuse this with air resistance (fluid friction), which increases dramatically with speed. Read the question carefully: if it mentions air or water, friction will depend on speed; on dry land, it won't. **Trap 4: Mixing Up Static and Kinetic Friction Values** — μₛ > μₖ always. If a question asks for maximum static friction but lists only the kinetic friction coefficient, you cannot solve it without additional information. Conversely, if you're given static friction, kinetic friction is smaller. **Trap 5: Ignoring the Direction of Friction** — Friction always opposes motion or tendency to move. A common trick: "A car accelerates forward—what direction does friction act?" Answer: forward (the tyres push the ground back; friction on tyres pushes forward). Friction does NOT always oppose the applied force; it opposes relative motion. **Trap 6: Forgetting g = 10 m/s² (or 9.8 m/s²)** — CBSE Class 9 problems typically use g = 10 m/s² for simplicity. If you use 9.8, your final answer may not match the given options. Check the question or options to infer which value is expected. **Trap 7: Choosing Options with Absolute Statements** — Phrases like "always," "never," and "all" are red flags. For example, "Friction always opposes motion"—this is true for kinetic friction but not static friction (which can act in any direction perpendicular to the surface if needed). Assertion-reason questions often use these absolute statements as traps. **Trap 8: Misreading Assertion-Reason Logic** — Even if both A and R are true, R must *explain* A for the answer to be option (A). If R is true but unrelated to A, the answer is (B). This nuance trips up many high-scoring students.

**Step 1: Scan and Categorize (First 2–3 minutes)** — Quickly read all questions. Mark 'easy' (direct recall, single formula), 'medium' (one calculation, conceptual combo), and 'hard' (multi-step, assertion-reason) with pencil. This prevents you from getting stuck on a hard question early and running out of time. **Step 2: Answer Easy Questions First (5–7 minutes for 10 questions)** — Solve direct questions about friction types, definitions, and basic formulas. Each should take ≤45 seconds. Record answers in the OMR sheet immediately; do NOT save them for later. **Step 3: Tackle Medium MCQs with Confidence (10–12 minutes for 10 questions)** — Use the friction equation f = μN methodically. Draw a quick diagram if the question involves an incline or multiple forces. Double-check units (N for force, dimensionless for μ). If you're unsure, eliminate two obviously wrong options first, then guess between the remaining two. **Step 4: Approach Assertion-Reason Pairs Methodically (12–15 minutes for 10 questions)** — Read the assertion and reason separately. Ask: (1) Is A true? (2) Is R true? (3) Does R *explain* A? Create a mental decision tree: If A = T and R = T and explains A → Answer is (A). If A = T and R = T but doesn't explain → Answer is (B). This systematic approach reduces error. For every assertion-reason pair, spend max 90 seconds. **Step 5: Review and Revise (Last 3–5 minutes)** — Go back to questions where you guessed or felt uncertain. Re-read once for misinterpretation. If a new answer is clearly correct, change it; otherwise, stick with your first choice (first instinct is often right). Do NOT flip-flop on every answer. **Bonus Tip: Formula Sheet Memorization** — Before the exam, memorize these friction formulas cold: - f = μN (kinetic and static) - N = mg (horizontal surface) - N = mg cos θ (inclined plane at angle θ) - Work against friction = f × d Having these automatic lets you spend brain energy on logic, not recall. **Bonus Tip: Elimination Strategy** — In a 4-option MCQ, at least one option is obviously wrong (e.g., a silly unit, a number far too large/small). Eliminate it immediately. You're now choosing between 3 options, doubling your odds if you guess. Use remaining options to spot the trap (see 'Common Trap Options' section above). **Real Exam Scenario:** You have 30 MCQs and 45 minutes (CBSE typical). That's 90 seconds per question on average. Easy MCQs (30 seconds), medium (60 seconds), hard/assertion-reason (90 seconds) = perfect balance. If you finish early, spend extra time on hard questions rather than reviewing easy ones (high return on investment).

You've now practiced 30 MCQs covering every friction concept in the CBSE Class 9 syllabus. But practice alone isn't enough—you need personalized feedback on *why* you chose wrong options and targeted re-teaching on weak areas. This is where adaptive learning shines. At cbsetutor.ai, our AI tutor analyzes your answer patterns, identifies misconceptions (e.g., thinking friction depends on surface area), and generates custom mini-lessons with worked examples. Our platform also tracks your progress, shows you which friction topics need more work (kinetic vs. static, inclined planes, fluid drag), and adapts difficulty in real time. Instead of grinding the same textbook chapter, you get a 1-on-1 tutor that knows exactly where you're stuck. Start a 3-day free trial at cbsetutor.ai—no credit card, no commitment. You'll get instant access to 500+ CBSE Class 9 MCQs, video lessons, and a personalized study plan. Your exam score will thank you.