Measurement of Time and Motion is the Eigth chapter in the new NCERT book of class 7 Science. This chapter covers the definition of motion, the difference between uniform and non-uniform motion, the calculation of speed using distance and time, and units like km/h and m/s. It also explores the measurement of time through history, the working of a simple pendulum, the concept of oscillation, and how to interpret distance-time graphs for moving objects. In this article, solutions to the NCERT questions have been provided.
Measurement of Time and Motion - NCERT Solutions
Q1. Calculate the speed of a car that travels 150 metres in 10 seconds. Express your answer in km/h.
Answer: First, we find the speed in metres per second:
Speed = Distance ÷ Time = 150 ÷ 10 = 15 m/s.
To change this to km/h, we multiply by 18/5.
Answer: First, we find the speed in metres per second:
Speed = Distance ÷ Time = 150 ÷ 10 = 15 m/s.
To change this to km/h, we multiply by 18/5.
Because, 1 km = 1000 m and 1 hour = 3600 s
15 × (18/5) = 3 × 18 = 54 km/h.
15 × (18/5) = 3 × 18 = 54 km/h.
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: Speed of the first runner = 400 ÷ 50 = 8 m/s.
Speed of the second runner = 400 ÷ 45 = 8.89 m/s.
The second runner is faster. The difference is 8.89 - 8 = 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: First, change the speed to km/h: 25 × (18/5) = 90 km/h.
Time = Distance ÷ Speed = 360 ÷ 90 = 4 hours.
Answer: First, change the speed to km/h: 25 × (18/5) = 90 km/h.
Time = Distance ÷ Speed = 360 ÷ 90 = 4 hours.
Q4. 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 4 h if it maintains the same speed throughout the journey?
Answer: (i) Speed = 180 ÷ 3 = 60 km/h.
(ii) To get m/s, multiply by 5/18: 60 × (5/18) = 16.67 m/s.
(iii) Distance in 4 hours = Speed × Time = 60 × 4 = 240 km.
Answer: (i) Speed = 180 ÷ 3 = 60 km/h.
(ii) To get m/s, multiply by 5/18: 60 × (5/18) = 16.67 m/s.
(iii) Distance in 4 hours = Speed × Time = 60 × 4 = 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: Let's change the train's speed to m/s: 72 × (5/18) = 20 m/s.
The train (20 m/s) is slightly faster than the horse (18 m/s).
Answer: Let's change the train's speed to m/s: 72 × (5/18) = 20 m/s.
The train (20 m/s) is slightly faster than the horse (18 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:
Answer:
- Uniform Motion: A car on an empty highway covers equal distances in equal time because it stays at a steady speed.
- Non-uniform Motion: A car in city traffic has to slow down, stop, and speed up, so it covers different distances in different time intervals.
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.
At 20 s, Distance = 16 m
At 40 s, Distance = 32 m (Already given)
At 50 s, Distance = 40 m (Already given)
At 60 s, Distance = 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 (60, 70, 50) in the same amount of time (1 hour).
Total distance = 60 + 70 + 50 = 180 km.
Total time = 3 hours.
Average speed = 180 ÷ 3 = 60 km/h.
Answer: The motion is non-uniform because the car covers different distances (60, 70, 50) in the same amount of time (1 hour).
Total distance = 60 + 70 + 50 = 180 km.
Total time = 3 hours.
Average speed = 180 ÷ 3 = 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 much more common. Examples:
Walking to a shop (you speed up or slow down to cross the road).
A school bus driving through morning traffic.
A kite flying in the wind.
Answer: Non-uniform motion is much more common. Examples:
Walking to a shop (you speed up or slow down to cross the road).
A school bus driving through morning traffic.
A kite flying in the wind.
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.
Average speed = Total distance (60m) ÷ Total time (100s) = 0.6 m/s.
Q11. 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:
Answer:
1. Time for first 500 m = 500 ÷ 10 = 50 s.
2. Time for next 500 m = 500 ÷ 5 = 100 s.
3. Remaining distance = 2000 - 500 - 500 = 1000 m.
4. Remaining time = 200 - 50 - 100 = 50 s.
5. Required speed for remaining part = 1000 ÷ 50 = 20 m/s.
6. Average speed for entire journey = 2000 m ÷ 200 s = 10 m/s.
2. Time for next 500 m = 500 ÷ 5 = 100 s.
3. Remaining distance = 2000 - 500 - 500 = 1000 m.
4. Remaining time = 200 - 50 - 100 = 50 s.
5. Required speed for remaining part = 1000 ÷ 50 = 20 m/s.
6. Average speed for entire journey = 2000 m ÷ 200 s = 10 m/s.