CBSE Class 7 Science Chapter 8: Measurement of Time and Motion — Assertion & Reason
CBSE Class 7 Science Assertion & Reason
Expert crafted · Instant PDF download · 2026-27
The following Assertion and Reason questions are based on Chapter 8: Measurement of Time and Motion from the NCERT Class 7 Science textbook Curiosity. Each question has four options — read both the Assertion (A) and Reason (R) carefully before selecting your answer.
How to attempt Assertion & Reason questions:
(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.
(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.
Assertion & Reason Questions
1
Assertion (A): Sundials determine time by tracking the changing position of an object's shadow cast by the Sun.
Reason (R): Early humans noticed that many events in nature, like the rising and setting of the Sun, repeat themselves after definite intervals of time.
Reason (R): Early humans noticed that many events in nature, like the rising and setting of the Sun, repeat themselves after definite intervals of time.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. While both statements are true historical facts about timekeeping, the repeating natural events are the basis for calendars and days, while the mechanism of a sundial specifically relies on the continuous movement of shadows during the day.
2
Assertion (A): The ancient Indian Ghatika-yantra was a type of water clock.
Reason (R): It consisted of a bowl with a fine hole at the bottom that floated on water and gradually filled up, sinking after a fixed time.
Reason (R): It consisted of a bowl with a fine hole at the bottom that floated on water and gradually filled up, sinking after a fixed time.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The predictable sinking time of the perforated bowl (taking exactly 24 minutes or one 'ghati') made it a reliable water clock for ancient timekeeping.
3
Assertion (A): The motion of a simple pendulum is considered periodic in nature.
Reason (R): A simple pendulum repeats its path after a fixed interval of time.
Reason (R): A simple pendulum repeats its path after a fixed interval of time.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. By definition, any motion that continuously repeats itself in equal, fixed time intervals is classified as periodic motion.
4
Assertion (A): The time taken by a pendulum to complete one full oscillation is called its time period.
Reason (R): The time period of a simple pendulum heavily depends on the mass of its metallic bob.
Reason (R): The time period of a simple pendulum heavily depends on the mass of its metallic bob.
Answer: (c)
A is true, but R is false. While A correctly defines the time period, the time period of a simple pendulum actually depends only on its length, not on the mass of the bob.
5
Assertion (A): Changing the heavy metal bob of a pendulum to a lighter one of the same length does not change its time period.
Reason (R): The time period of a simple pendulum of a given length is constant at a specific place.
Reason (R): The time period of a simple pendulum of a given length is constant at a specific place.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Since mass does not affect the swing, any pendulum of the exact same length will consistently have the same time period.
6
Assertion (A): Christiaan Huygens invented the first pendulum clock in 1656.
Reason (R): Huygens was inspired by Galileo's observation that a pendulum of a given length always takes the same time to complete one oscillation.
Reason (R): Huygens was inspired by Galileo's observation that a pendulum of a given length always takes the same time to complete one oscillation.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Galileo's fundamental discovery about the constant time period of pendulums provided the scientific basis for Huygens to engineer an accurate mechanical clock.
7
Assertion (A): Modern quartz clocks and atomic clocks measure time using periodically repeating processes.
Reason (R): Modern clocks rely on the continuous flow of water or sand to mark equal intervals of time.
Reason (R): Modern clocks rely on the continuous flow of water or sand to mark equal intervals of time.
Answer: (c)
A is true, but R is false. Modern clocks do use repeating processes, but they rely on tiny, rapid vibrations from quartz crystals or specific atoms, not water or sand (which were used in ancient clocks).
8
Assertion (A): The symbol for the SI unit of time should be written as a capital 'S'.
Reason (R): The SI unit of time is the second.
Reason (R): The SI unit of time is the second.
Answer: (d)
A is false, but R is true. The SI unit of time is the second, but its correct symbol is written as a lowercase 's'.
9
Assertion (A): Five hours should be written as '5 h' and not '5 hrs'.
Reason (R): Symbols for units are always written in singular form and do not take a plural 's'.
Reason (R): Symbols for units are always written in singular form and do not take a plural 's'.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. By standard scientific convention, unit symbols like 'h', 'min', and 's' are never pluralised.
10
Assertion (A): An object that covers a larger distance in the same amount of time compared to another object is moving faster.
Reason (R): The distance covered by an object in a unit time is defined as its speed.
Reason (R): The distance covered by an object in a unit time is defined as its speed.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Because speed is the ratio of distance to time, covering more distance in the same time mathematically results in a higher speed.
11
Assertion (A): The speed of an object can be calculated if we know the total distance covered and the total time taken.
Reason (R): Speed = Total time taken ÷ Total distance covered.
Reason (R): Speed = Total time taken ÷ Total distance covered.
Answer: (c)
A is true, but R is false. We can calculate speed with those two values, but the formula is Speed = Total distance covered ÷ Total time taken, not the other way around.
12
Assertion (A): The SI unit of speed is kilometre per hour (km/h).
Reason (R): Speed is the ratio of distance and time, so its basic SI unit is metre per second (m/s).
Reason (R): Speed is the ratio of distance and time, so its basic SI unit is metre per second (m/s).
Answer: (d)
A is false, but R is true. While km/h is a common unit for vehicle speed, the official SI unit is metre/second (m/s) because the SI units for length and time are metre and second.
13
Assertion (A): The instrument in a vehicle that displays its speed in km/h is called a speedometer.
Reason (R): An odometer is an instrument fitted in vehicles that measures the total distance travelled.
Reason (R): An odometer is an instrument fitted in vehicles that measures the total distance travelled.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both statements are correct definitions of the instruments found on a vehicle's dashboard, but they serve two distinct independent functions.
14
Assertion (A): A car moving on a straight, empty highway at a constant speed of 60 km/h is in uniform linear motion.
Reason (R): An object moving along a straight line with an unchanging, constant speed is said to be in uniform linear motion.
Reason (R): An object moving along a straight line with an unchanging, constant speed is said to be in uniform linear motion.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The car strictly meets the criteria for uniform linear motion because both its path (straight) and its speed (constant 60 km/h) are unchanging.
15
Assertion (A): A train travelling between two stations is generally an example of uniform linear motion.
Reason (R): The speed of a train keeps changing as it starts, speeds up, slows down, and stops at stations.
Reason (R): The speed of a train keeps changing as it starts, speeds up, slows down, and stops at stations.
Answer: (d)
A is false, but R is true. Because the train's speed continuously changes (as described in R), its motion is non-uniform, not uniform.
16
Assertion (A): An object in non-uniform linear motion covers unequal distances in equal intervals of time.
Reason (R): The speed of an object in non-uniform motion keeps changing continuously.
Reason (R): The speed of an object in non-uniform motion keeps changing continuously.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Because the object is speeding up or slowing down, it naturally travels different distances during the exact same time frames.
17
Assertion (A): In everyday life, we mostly use the term 'average speed' when discussing the motion of vehicles.
Reason (R): Vehicles seldom move with a constant speed over long distances or long intervals of time.
Reason (R): Vehicles seldom move with a constant speed over long distances or long intervals of time.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Because traffic, turns, and stops force vehicles to constantly change speed (non-uniform motion), we calculate their overall journey using average speed.
18
Assertion (A): If a car travels at an average speed of 50 km/h for 2 hours, the total distance covered is 100 km.
Reason (R): Total distance covered is calculated by multiplying the speed by the total time taken.
Reason (R): Total distance covered is calculated by multiplying the speed by the total time taken.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Rearranging the speed formula (Distance = Speed × Time) gives 50 km/h × 2 h = 100 km.
19
Assertion (A): If a train has to cover 360 km at an average speed of 90 km/h, it will take 4 hours.
Reason (R): Total time taken can be calculated by dividing the total distance covered by the speed.
Reason (R): Total time taken can be calculated by dividing the total distance covered by the speed.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Using the formula Time = Distance ÷ Speed, dividing 360 km by 90 km/h correctly results in 4 hours.
20
Assertion (A): A child swinging back and forth on a playground swing undergoes oscillatory motion.
Reason (R): The swing repeatedly moves from one extreme position to another through its central mean position, acting like a simple pendulum.
Reason (R): The swing repeatedly moves from one extreme position to another through its central mean position, acting like a simple pendulum.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The physical mechanics of a swing are identical to those of a simple pendulum, making its repetitive back-and-forth movement a classic example of oscillatory motion.
❓ Frequently Asked Questions
What is covered in CBSE Class 7 Science Chapter 8 Measurement of Time and Motion?
This chapter covers all key topics from Measurement of Time and Motion as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 7 board exam preparation covering the complete syllabus.
Are these CBSE Class 7 Science Assertion & Reason updated for 2026-27?
Yes, all content at eBookPublisher is updated as per the latest 2026-27 CBSE syllabus.
How many chapters are in CBSE Class 7 Science?
All chapters of CBSE Class 7 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
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