Class 9 Science Chapter 9 Motion and Time Previous Year Questions (2020–2025)

Reading Chapter 9 three times won't improve your score—but solving past papers will. Here's why: (1) **Repetition reveals patterns.** CBSE doesn't ask wildly random questions. They repeat concepts in similar forms. If you've seen 'Calculate speed from a distance-time graph' five times in different PYQs, you'll recognize it instantly on exam day. (2) **You learn to manage time.** A 1-mark question should take 30 seconds; a 5-mark solution, 8–10 minutes. Only timed practice teaches this. (3) **You spot your weakness early.** If you solve a 3-mark speed question and get it wrong, you know immediately whether your formula knowledge is weak or your arithmetic is shaky. Theory reading doesn't give you this feedback. (4) **Confidence grows fast.** When you've solved the same question type three times, you walk into the exam room calm. This chapter includes straightforward calculations (unlike geometry), so repeated exposure directly boosts your marks. Start with 1-mark questions to warm up, then move to 3 and 5-mark problems. Time yourself.

These short questions test definitions, basic units, and recognition. They appear almost every year in slightly different wording. **Q1: Define uniform motion.** A: Motion in which an object covers equal distances in equal intervals of time, in a straight line, with constant velocity. **Q2: A car travels 60 km in 1.5 hours. What is its speed?** A: Speed = Distance ÷ Time = 60 ÷ 1.5 = 40 km/h **Q3: What is the SI unit of speed?** A: metre per second (m/s) **Q4: If the distance-time graph is a straight horizontal line, what does it mean?** A: The object is at rest (zero velocity). **Q5: Name the device used to measure time accurately in the laboratory for a simple pendulum experiment.** A: Stop clock or stopper (to measure the period of oscillation). **Key insight:** These questions reward quick recall. Write out definitions in full sentences during revision—one-word answers cost marks. Practise unit conversion (km/h ↔ m/s) separately.

3-mark questions blend calculation with explanation. They typically ask you to draw a conclusion from data or solve a two-step problem. **Q1: A student measured the time period of a simple pendulum as 1.8 seconds using a stop clock. Is this a reliable measurement? Explain why.** A: No, measuring only one oscillation is unreliable because stop clock reaction time is ~0.1 s, which is a large error relative to 1.8 s. Instead, measure the time for 20 oscillations (say, 36 seconds), then divide by 20 to get the period. This reduces error to ~0.005 s per oscillation. (3 marks: concept of systematic error, correct method, calculation of reduced error) **Q2: A distance-time graph shows a curved line rising steeply. What type of motion is this? Explain.** A: Non-uniform (accelerated) motion. In a distance-time graph, a straight line means constant speed. A curve means the slope (speed) is changing—the object is moving faster as time progresses. The steeper curve indicates acceleration. (3 marks: identification, explanation of graph interpretation, definition of acceleration) **Q3: Object A travels 50 m in 5 s; Object B travels 80 m in 10 s. Which is faster?** A: Speed of A = 50 ÷ 5 = 10 m/s. Speed of B = 80 ÷ 10 = 8 m/s. Object A is faster. (3 marks: correct formula application for both, comparison, correct answer) **Q4: A train travels at 60 km/h for the first 2 hours and 80 km/h for the next 3 hours. What is its average speed?** A: Distance in first 2 hours = 60 × 2 = 120 km. Distance in next 3 hours = 80 × 3 = 240 km. Total distance = 120 + 240 = 360 km. Total time = 2 + 3 = 5 hours. Average speed = 360 ÷ 5 = 72 km/h. (3 marks: distance calculation for each segment, total distance, average speed formula, final answer) **Q5: Explain why the motion of a car in a busy city is non-uniform.** A: The car must stop at traffic lights, accelerate from rest, and brake repeatedly. Its speed is constantly changing due to traffic conditions. Equal intervals of time do not correspond to equal distances covered. Therefore, it exhibits non-uniform motion. (3 marks: identification of causes, definition contrast, real-world example)

5-mark questions demand multi-step reasoning, graph interpretation, or practical application. These carry significant weight. **Q1: An athlete runs 100 m in 10 seconds. (a) Calculate the speed. (b) If the athlete runs at this constant speed, how long will it take to cover 250 m? (c) Draw a distance-time graph for the motion and explain what the slope represents.** **Solution:** (a) Speed = Distance ÷ Time = 100 ÷ 10 = 10 m/s. (1 mark) (b) Time = Distance ÷ Speed = 250 ÷ 10 = 25 seconds. (1.5 marks: correct formula, substitution, answer) (c) Distance-time graph: x-axis = Time (s), y-axis = Distance (m). Points: (0, 0), (5, 50), (10, 100), (15, 150), (20, 200), (25, 250). A straight line through these points. (1.5 marks: correct axes labelling, accurate points, straight line) Explanation: The slope of the distance-time graph represents speed. Since the line is straight, the slope is constant, confirming uniform motion at 10 m/s. A steeper slope = higher speed; a flatter slope = lower speed. (1 mark: correct identification of slope as speed, explanation) **Q2: A simple pendulum has a time period of 2 seconds. (a) What is the frequency? (b) If the length is increased, how will the time period change? (c) Design an experiment to measure the time period accurately using a stop clock.** **Solution:** (a) Frequency = 1 ÷ Time Period = 1 ÷ 2 = 0.5 Hz. (1 mark) (b) If length increases, the time period increases (T ∝ √L). This is because a longer pendulum swings slower. (1 mark: correct relationship, brief explanation) (c) Experiment design (1.5 marks): — Suspend the pendulum from a rigid support. — Displace it slightly (< 15°) and release. — Start the stop clock when the bob passes the mean position. — Count 20 complete oscillations. — Stop the clock when the bob returns to the same position after 20 oscillations. — Record the time (e.g., 40 seconds for 20 oscillations). — Time period = Total time ÷ Number of oscillations = 40 ÷ 20 = 2 seconds. — Repeat 3 times and find the average. Why measure 20 oscillations? This reduces the fractional error introduced by stop clock reaction time (±0.1 s) from ~5% to ~0.25%. (1.5 marks: clear procedure, error reduction explanation, calculation) **Q3: Two vehicles travel on the same road. Vehicle A's motion is shown by a straight line on a distance-time graph. Vehicle B's motion is shown by a curved line that becomes steeper over time. (a) Describe the motion of each vehicle. (b) Calculate Vehicle A's speed if it covers 150 m in 6 seconds. (c) What does the increasing slope of Vehicle B's graph tell you about its acceleration?** **Solution:** (a) Vehicle A: Uniform (constant) motion. Speed is constant throughout the journey, so distance increases uniformly with time. Vehicle B: Non-uniform (accelerated) motion. Speed increases over time; the vehicle is accelerating. (1.5 marks: correct identification, reasoning for each) (b) Speed of A = Distance ÷ Time = 150 ÷ 6 = 25 m/s. (1 mark: formula, calculation, unit) (c) The slope of a distance-time graph represents speed (or velocity in the direction of motion). An increasing slope means the speed is increasing—Vehicle B is undergoing positive acceleration. The rate at which the slope increases indicates the magnitude of acceleration. A rapidly steepening curve = high acceleration; a gradually steepening curve = low acceleration. (2.5 marks: correct interpretation of slope, definition of acceleration, relationship between curve shape and acceleration magnitude)

The latest CBSE reforms emphasize competency-based learning and reduced rote memorization. For Chapter 9, expect these shifts: (1) **Fewer pure definition questions.** 1-mark questions now often ask 'Why do we measure 20 oscillations instead of 1?' rather than 'Define uniform motion?' This tests conceptual depth, not memory. (2) **More real-world scenarios.** Expect questions like 'A train's speed-time graph shows it accelerating, then moving at constant speed, then decelerating. Describe the journey.' These blend graph reading with practical reasoning. (3) **Emphasis on precision in measurement.** Questions now reward students who understand error reduction. For pendulum experiments, examiners specifically ask 'Why count 20 oscillations?' and expect the answer: 'To reduce percentage error in time measurement.' (4) **Distance-time and speed-time graphs together.** The 2026–27 pattern is likely to ask students to sketch both graphs for the same motion or compare them. Practice drawing both for the same scenario (e.g., accelerating car: straight line on distance-time, curved line on speed-time). (5) **Interdisciplinary links.** Expect connections to Chapter 8 (Motion) or Chapter 10 (Gravitation). For instance, 'A pendulum's time period changes as you move from Earth to the Moon. Why?' (Links to gravitational field strength.) To prepare, focus on *why* concepts work, not just *what* they are. Start a 3-day free trial at cbsetutor.ai to access AI-coached practice on these evolving patterns.

Time management makes or breaks your score on Motion and Time. Here's a battle-tested strategy: (1) **Read all questions first (2 minutes).** Don't start solving immediately. Read the entire question paper, underline key data (numbers, 'explain', 'draw'), and mentally flag which questions you're confident on. (2) **Solve 1-mark questions first (5 minutes max).** These are 'gimmes' if you've revised definitions. Don't second-guess yourself. One sentence per answer. (3) **Tackle numerical 3-mark questions next (12 minutes for 4 questions).** Write the formula, show substitution, write the answer with units. Examiners give 1 mark for formula, 1 for correct substitution, 1 for correct answer—even if your arithmetic is slightly off, partial credit is automatic if you show work. (4) **Then do explanatory 3-mark questions (8 minutes).** For 'explain' or 'describe' questions, write in 3–4 clear sentences. One point per sentence typically earns one mark. (5) **Attempt 5-mark questions last (15 minutes for 3 questions).** These carry weight but are time-intensive. If you're running low on time, attempt them partially: even a correct formula or a well-drawn graph earns 1–2 marks. (6) **Graph questions: Draw first, explain second.** Always label axes (with units), mark key points, draw the line/curve carefully. Explanation comes after—don't waste time writing analysis before drawing. (7) **Double-check units.** Speed in m/s? Distance in m, time in s? A correct answer without units loses a mark. (8) **Flag 'non-uniform motion' and 'acceleration' questions.** These require deeper thinking. If stuck, write what you know (e.g., 'In non-uniform motion, the distance covered in equal time intervals is unequal') and leave it—don't blank it out.

Use this checklist in the 48 hours before your Science paper: ✓ Definitions: Write out uniform motion, non-uniform motion, speed, velocity, acceleration, time period, frequency. ✓ Formulas: Memorize Speed = Distance ÷ Time, Average Speed = Total Distance ÷ Total Time, Frequency = 1 ÷ Time Period. ✓ Unit conversions: Convert 36 km/h to m/s (= 10 m/s). Convert 15 m/s to km/h (= 54 km/h). Practice 5 conversions. ✓ Distance-time graphs: Sketch a straight line (uniform motion), a curved line (acceleration), and a horizontal line (at rest). Label axes and slopes. ✓ Pendulum experiment: Write out the full procedure (20 oscillations, why 20, how to find period). Understand why longer = slower. ✓ Numerical practice: Solve at least 10 speed, distance, and time problems. Include two-step problems (e.g., two segments with different speeds). ✓ Explanation practice: For 3 questions, write 3-sentence explanations of why something happens (not just what happens). ✓ Exam timing: Time yourself solving a mixed 13-question set (1, 3, 5-mark questions) in 60 minutes. Aim for 5 min for 1-mark, 10 min for 3-mark, 15 min for 5-mark. If you complete this checklist, you've covered every concept, question type, and skill this chapter tests.