Class 7 Science Chapter 8: Measurement of Time and Motion NCERT Solutions

Question 1.
How was time measured when there were no clocks and watches? (Page 106)

Answer:

Before clocks and watches were invented, people measured time using devices such as sundials, water clocks, hourglasses, and candle clocks.

Question 2.

For races covering the same distance, we can tell who was faster by measuring time. But how can we tell that when comparing races for different distances? (Page 112)

Answer: If two racers cover the same distance, the one who takes less time is considered faster.

Question 3.

I once watched a part of marathon on a straight road stretch. I noticed that some people seemed to be running at the same speed during that distance while some people would speed up or slow down. How were their motion different? (Page 116)

Answer: People moving at a constant speed show uniform motion, while those whose speed increases or decreases have non-uniform motion.

Speed = 25 m/s
Distance = 360 km = 3,60,000 m
Time taken = \(\dfrac{\text { Distance }}{\text { Speed }}\) = \(\dfrac{3,60,0000 \mathrm{~m}}{25 \mathrm{~m} / \mathrm{s}}\)
= 14,400s
⇒ 240 mins
⇒ 4 hours

Question 4.
A train travels 180 km in 3 h. Find its speed in:

(i) km/h
(ii) m/s
(iii) What distance will it travel in 4h if it maintains the same speed throughout the journey?

Answer:
Distance = 180 km, time = 3h
(i) Speed = \(\dfrac{\text { Distance }}{\text { Time }}=\dfrac{180 \mathrm{~km}}{3 \mathrm{~h}}\) = 60 Km/h
(ii) Speed in m/s= 60 × \(\dfrac{5}{18}\) = 16.677 m/s
(iii) Time = 4h, Speed = 60 km/h
Distance = Speed × Time
= 60 × 4 = 240 km

Question 5.
The fastest galloping horse can reach the speed of approximately 18 m/s. How does this compare to the speed of a train moving at 72 km/h?

Speed of horse = 18 m/s
Speed of train = 72 km/h = 72 × \(\dfrac{5}{18}\) = 20 m/s
The train is faster by 2 rn/s than the fastest galloping horse.

Question 6.
Distinguish between uniform and non-uniform motion using the example of a car moving on a straight highway with no traffic and a car moving in city traffic.

Answer:

Uniform motion:
An object is said to be in uniform motion if it covers equal distances in equal intervals of time. For example, a car moving smoothly on a straight highway without traffic shows uniform motion.

Non-uniform motion:
An object is said to be in non-uniform motion if it covers unequal distances in equal intervals of time. For instance, a car moving through traffic shows non-uniform motion.

Question 7.
Data for an object covering distances in different intervals of time are given in the following table. If the object is in uniform motion, fill in the gaps in the table.

Answer:

In uniform motion, an object covers equal distances in equal intervals of time. Therefore, its speed remains constant throughout the motion.

From the table, the object travels 8 metres every 10 seconds, which means its speed remains constant at 0.8 m/s during the entire motion.

Question 8.
A car covers 60 km in the first hour, 70 km in the second hour, and 50 km in the third hour. Is the motion uniform? Justify your Answer:

Find the average speed of the car.

The car covers different distances in each hour. Hence, the motion of the car is nonuniform.
Total distance = 60 km + 70 km + 50 km = 180 km
Total time = 3 hours

Average speed = \(\dfrac{\text { Total distance travelled }}{\text { Total time taken }}\)
= \(\dfrac{180 \mathrm{~km}}{3 \mathrm{~h}}\) = 60 km/h.
Hence, the average speed of the car is 60 km/h.

Question 9.
Which type of motion is more common in daily life—uniform or non-uniform? Provide three examples from your experience to support your answer.

Answer:

In everyday life, most motions are non-uniform because objects do not move at a constant speed all the time. Their speed keeps changing due to reasons such as traffic, uneven or rough roads, and various obstacles.

Examples:

• Travelling in a bus on an uneven road

• Playing cricket

• Walking through a crowded market

Question 10.
Data for the motion of an object are given in the following table. State whether the speed of the object is uniform or non-uniform. Find the average speed.

The object exhibits non-uniform motion, because it covers unequal distances in equal time intervals.

Total distance travelled = 60 m
Total time taken = 100 s
Average speed = \(\dfrac{Total distance}{Total time taken}\)
= \(\dfrac{60}{100}\)
= 0.6 m/s

Question 11.
A vehicle moves along a straight line and covers a distance of 2 km. In the first 500 m, it moves with a speed of 10 m/s and in the next 500 m, it moves with a speed of 5 m/s. With what speed should it move the remaining distance so that the journey is complete in 200 s? What is the average speed of the vehicle for the entire journey?

Answer:
Given
Total distance = 2 km = 2000 m,
Total time = 200
Step 1: Time taken to cover the first 500 m
Time = \(\dfrac{\text { Distance }}{\text { Speed }}\) = \(\dfrac{500}{10}\) = 50 s

Step 2: Time taken to cover the next 500 m
Time = \(\dfrac{500}{10}\) = 100 s

Step 3: Remaining distance = 2000 – 1000 = 1000 m
Remaining time = 200 – 150 = 50 s

Step 4: Speed required to cover the remaining 1000 m
Speed = \(\dfrac{1000}{50}\) = 20 m/s

Step 5: Average speed = \(\dfrac{Total distance}{Total time taken }\) = \(\dfrac{2000}{200}\) = 10 m/s

Activity 8.1: Let Us Construct (Page 107)

Answer:
Students should do it by themselves.

Activity 8.2: Let us Experiment (Pages 109-110)

Answer:
Students should do it by themselves.

Activity 8.3: Let Us Identify (Page 112)

Look at the wall clock shown in Fig. 8.9 carefully. What is the smallest interval of time you can measure with it?

One second is the smallest interval of time that we can measure using this clock.

Activity 8.4: Let Us Calculate (Pages 114-115)

Table 8.2: Finding the speed of trains Name of the railway station nearest to your place of stay Delhi.

Understanding Measurement of Time and Motion in Science Class 7

Mastering the Measurement of Time and Motion is essential for building a strong foundation in Class 7 Science. Knowing about devices like pendulum clocks and sundials helps you understand how humans have tracked time through history.

Remember that the SI unit of time is the second and for speed, it is meter per second. Focusing on key concepts like speed and types of motion can make your exam preparation much easier and more effective.

Stay curious like Prerna and practice the exercise questions from NCERT. Regular revision and real-life examples will help you gain confidence and score high marks in Science Chapter 8 for the 2025-26 session.