RBSE Class 7 Science Chapter 8 Solutions in English — Measurement of Time and Motion

RBSE Class 7 Science Chapter 8 Question Answer Measurement of Time and Motion

By tackling theseRBSE Solutions Class 7 Scienceand RBSE Class 7 Science Chapter 8 Measurement of Time and Motion Question Answer, students will build a solid foundation in the topic.

Measurement of Time and Motion Class 7 Question Answer

RBSE Class 7 Science Chapter 8 Measurement of Time and Motion Question Answer

Class 7 Science Curiosity Chapter 8 Question Answer (Exercise)

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Question 1.
Calculate the speed of a car that travels 150 meters in 10 seconds. Express your answer in km/h.
Answer:
Distance covered =150 m
Time taken = 10 s
Distance 150 m .
Speed = $\frac{\text { Distance }}{\text { Time }}$ = $\frac{150 \mathrm{~m}}{10}$ = 15 m/s
∵ 1 m/s = 3.6 Km/h
Speed is = 15 x 3.6 Km/h
= 54 Km/h

Question 2.
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 = $\frac{\text { Distance }}{\text { Time }}$
First runner = $\frac{400}{50}$ = 8 m/s
Second runner = $\frac{400}{45}$ = 8.89 m/s
So, second runner had a greater speed of 8.89 – 8.00 = 0.89 m/s

Question 3.
A train travels at a speed of 25 m/s and covers a distance of 360 km. How much time does it take?
Answer:
1 m/s = 3.6 km/h
25 m/s = 25 × 3.6 = 90 km/h
Time = $\frac{\text { Distance }}{\text { Time }}$ = $\frac{360 \mathrm{~km}}{90 \mathrm{~km} / \mathrm{h}}$ = 4 hours
Train will take 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 4 h if it maintains the same speed throughout the journey?
Answer:
(i) Speed = $\frac{\text { Distance }}{\text { Time }}$
= $\frac{180 \mathrm{~km}}{3 \mathrm{~h}}$ = 60 km/h

(ii) 1 km = 1000 metes
1 hour = 3600s
⇒ 60 × 1000/3600
= 16.67 m/s

(iii) 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?
Answer:
Speed of train
= 72 km/h = $\frac{72 \times 1000}{3600}$ = 20 m/s
Speed of horse
= 18 m/s
Speed of train is greater than horse
= 20 – 18 = 2 m/s

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 :
When an object covers same distance in same time periods then it is called uniform motion.
Ex.: A car moving on a straight highway with no traffic. Because it is moving on a constant speed.

Non-uniform motion :
When an object covers different distances in same time period, is called non-uniform motion.
Ex. : Car moving in city traffic, because it move sometimes and stop sometimes.

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:

When an object moves to same distance in same time period, then it is called uniform motion.
According to Table :
• Distance travelled in 0-10 sec. = 8 m
• Distance travelled in 10-20 sec. = 8 m
• Distance travelled in 20-30 sec. = 8 m
• Distance travelled in 30-40 sec. = 8 m
• Distance travelled in 40-50 sec. = 8 m
• Distance travelled in 50-60 sec. = 8 m
• Distance travelled in 60-70 sec. = 8 m

Question 8.
A car covers 60 km in the first hour, 70 km in second hour, and 50 km in third hour. Is the motion uniform? Justify your answer. Find the average speed of car.
Answer:
Distance travelled by first car = 60 km
Distance travelled by second car = 70 km
Distance travelled by third car = 50 km
The distances travelled are not uniform because the distances travelled in every hour is different.

Total distance – 60 + 70 + 50 = 180 km
Total time = 3 hour

Total distance
So, Average speed = $\frac{180}{3}$
= $\frac{180}{3}$ = 60 km/hr

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:
Generally non-uniform motion is common in daily life like:

1. Bus or auto-rikshaw moving on road runs fast sometime and slow other time.
2. Pedestrian on road have variations in speed.
3. Cycle in market crowd.

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.

Answer:
According to data speed of object is nonuniform, because the distance travelled in same time period are different.
Average speed = Total distance ÷ Total time
Total distance = 60 m
Total time = 100 s
Average speed = 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 200s? What is the average speed of the vehicle for the entire journey?
Answer:
Time = [/latex]\frac{\text { Distance }}{\text { Speed }}[/latex]
Time on first 500 m = [/latex]\frac{\text { 500 }}{\text { 10 }}[/latex] = 50 sec.
Time on next 500 m = [/latex]\frac{\text { 500 }}{\text { 5 }}[/latex] = 100 sec.
⇒ Total time till yet = 150 s
⇒ Remaining time = 200 – 150 = 50 s

Remaining distance
Total distance = 2000 m
Distance in first part + second part = 1000 m
⇒ Remaining distance = 1000 m Required speed for remaining distance
⇒ Speed = [/latex]\frac{\text { Distance }}{\text { Speed }}[/latex]

Average speed for complete journey
Average speed = Total distance ÷ Total time
= $\frac{2000}{200}$ = 10 m/s

Measurement of Time and Motion Class 7 Questions and Answers (Intext)

(Page No. 106)

Question 1.
How was time measured when there were no clocks and watches?
Answer:
In that time, time was measured by natural events which are repeated after a time period, e.g., sunrise, sunset, phases of moon and the changing seasons.

(Page No. 112)

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?
Answer:
We will tell who ran faster by calculating the ratio of distance covered in a time period.

(Page No. 116)

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?
Answer:
Those people are not in an uniform motion. When an object or person moves along a straight line with a constant speed is said to be in uniform linear motion and when a person or object moving in straight line but keeps speed changing called it non-uniform linear motion.