NCERT Solutions for Class 7 Science Curiosity Chapter 8: Measurement of Time and Motion by PW
A moving vehicle, a running athlete or a travelling train may cover different distances in different amounts of time. Understanding such situations requires you to connect distance, time and speed correctly. Many questions in this chapter involve calculations, unit conversions and comparisons between objects moving at different speeds. Identifying uniform and non-uniform motion and calculating average speed can also be confusing when the given values need to be interpreted carefully.
The NCERT Solutions Class 7 Science Curiosity Chapter 8 explain these concepts through clear answers and step-by-step calculations. They cover speed, distance, time, unit conversion, uniform and non-uniform motion, average speed and practical examples of motion.
Class 7 Science Curiosity Chapter 8 Solutions
The following solutions cover the textbook questions on speed, distance, time and different types of motion.
Q1. Calculate the speed of a car that travels 150 metres in 10 seconds. Express your answer in km/h.
Answer:
Given:
-
Distance = 150 m
-
Time = 10 s
Using the formula:
Speed = Distance ÷ Time
Speed = 150 ÷ 10 = 15 m/s
To convert m/s into km/h:
15 × 18/5 = 54 km/h
Answer: 54 km/h
The conversion rules are:
-
m/s to km/h: multiply by 18/5
-
km/h to m/s: multiply by 5/18
Q2. A runner completes 400 metres in 50 seconds. Another runner completes the same distance in 45 seconds. Who has a greater speed and by how much?
Answer:
For Runner A:
Distance = 400 m
Time = 50 s
Speed of Runner A = 400 ÷ 50 = 8 m/s
For Runner B:
Distance = 400 m
Time = 45 s
Speed of Runner B = 400 ÷ 45 ≈ 8.89 m/s
Difference in speed:
8.89 − 8 = 0.89 m/s
Answer: Runner B has the greater speed by approximately 0.89 m/s.
Q3. A train travels at a speed of 25 m/s and covers a distance of 360 km. How much time does it take?
Answer:
Given:
-
Speed = 25 m/s
-
Distance = 360 km
First, convert the speed into km/h:
25 × 18/5 = 90 km/h
Using:
Time = Distance ÷ Speed
Time = 360 ÷ 90 = 4 hours
Answer: 4 hours
Q4. A train travels 180 km in 3 h. Find its speed in:
(i) km/h
Answer:
Distance = 180 km
Time = 3 h
Speed = Distance ÷ Time
Speed = 180 ÷ 3 = 60 km/h
Answer: 60 km/h
(ii) m/s
Convert 60 km/h into m/s:
60 × 5/18 = 16.67 m/s
Answer: 16.67 m/s
(iii) What distance will it travel in 4 h if it maintains the same speed throughout the journey?
Answer:
Speed = 60 km/h
Time = 4 h
Using:
Distance = Speed × Time
Distance = 60 × 4 = 240 km
Answer: 240 km
Q5. 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?
Answer:
Speed of horse = 18 m/s
Speed of train = 72 km/h
Convert the train's speed into m/s:
72 × 5/18 = 20 m/s
Difference:
20 − 18 = 2 m/s
Answer: The train is faster than the horse by 2 m/s.
Q6. 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 |
Non-uniform Motion |
|
An object covers equal distances in equal intervals of time. |
An object covers unequal distances in equal intervals of time. |
|
Its speed remains constant. |
Its speed changes with time. |
|
Example: A car moving on a straight highway without traffic at a constant speed. |
Example: A car moving through city traffic while slowing down, stopping or speeding up. |
Q7. 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:
The object covers 8 m every 10 seconds.
|
Time (s) |
0 |
10 |
20 |
30 |
40 |
50 |
60 |
70 |
|
Distance (m) |
0 |
8 |
16 |
24 |
32 |
40 |
48 |
56 |
Therefore, the missing values are:
-
Distance at 20 s = 16 m
-
Time corresponding to 32 m = 40 s
-
Distance at 60 s = 48 m
-
Time corresponding to 48 m = 60 s
The speed of the object is:
Speed = 8 ÷ 10 = 0.8 m/s
Answer: 40 s, 16 m, 60 s and 48 m.
Q8. 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.
Answer:
The motion is non-uniform because the car covers different distances during equal intervals of time.
Total distance:
60 + 70 + 50 = 180 km
Total time = 3 hours
Average speed:
Average speed = Total distance ÷ Total time
= 180 ÷ 3
= 60 km/h
Answer:
-
Motion = Non-uniform
-
Average speed = 60 km/h
Q9. 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:
Non-uniform motion is more common in daily life because the speed of moving objects frequently changes.
Examples:
-
A vehicle slows down or stops when an animal comes onto the road.
-
A vehicle changes its speed or stops in traffic.
-
A vehicle slows down while passing over potholes.
Q10. 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.
Answer:
|
Time (s) |
0 |
10 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
|
Distance (m) |
0 |
6 |
10 |
16 |
21 |
29 |
35 |
42 |
45 |
55 |
60 |
The speed is non-uniform because the object does not cover equal distances in equal intervals of time.
Total distance = 60 m
Total time = 100 s
Average speed:
Average speed = Total distance ÷ Total time
= 60 ÷ 100
= 0.6 m/s
Answer:
-
Speed = Non-uniform
-
Average speed = 0.6 m/s
NCERT Solutions for Class 7 Science Curiosity Chapter 8 PDF
For quick access during revision, having the chapter’s numerical questions and key concepts in one resource can make practice easier. The Class 7 Science Curiosity Chapter 8 Solutions PDF covers speed, distance, time, unit conversions, uniform and non-uniform motion, and average-speed questions.
NCERT Solutions for Class 7 Science Curiosity Chapter 8 PDF
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How Can NCERT Class 7 Science Chapter 8 Solutions by PW Help in Learning?
The NCERT Class 7 Science Chapter 8 Solutions by PW make topics related to time, distance and motion easier to understand through numerical questions, examples and clear explanations. Key learning areas include:
-
Learn Speed Calculation: Understand how distance and time are related to the speed of a moving object.
-
Master Unit Conversions: Practise converting speed from m/s to km/h and vice versa.
-
Identify Different Motions: Distinguish between uniform and non-uniform motion using familiar situations.
-
Work Out Average Speed: Understand how total distance and total time are used to find average speed.
-
Practise Numerical Questions: Solve problems based on cars, trains, runners and other moving objects.
-
Read Motion Data: Analyse distance-time tables to identify changes in speed and patterns of motion.
-
Use Concepts in Daily Life: Relate measurements of time, distance and speed to everyday situations.
-
Follow Accurate Calculations: Apply the correct formulas, units and calculation steps while solving problems.
Understanding how objects move becomes easier when distance, time and speed are studied together. The NCERT Class 7 Science Chapter 8 Solutions explain numerical questions on speed, unit conversion, uniform and non-uniform motion and average speed with clear calculations. Practising these questions can help children apply the concepts correctly and improve accuracy while solving problems related to motion.
Related Resources
NCERT Solutions for Class 7 Science Curiosity Chapter 8 FAQs
What is the main topic of Chapter 8 in the Class 7 Science Curiosity textbook?
How was time measured before the invention of clocks and watches?
What is uniform motion?
What is non-uniform motion?
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