Measurement of Time and Motion Class 7 Questions and Answers Science Chapter 8

Students can use Curiosity Class 7 Science Book Solutions Chapter 8 Measurement of Time and Motion Class 7 Question and Answer as a quick reference guide.

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

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

Measurement of Time and Motion Class 7 Question Answer (InText)

Question 1.
How was time measured when there were no clocks and watches? (Page 106)
Answer:
Before the invention of clocks and watches, time was measured using instruments like sundials, water clocks, hourgiasses and candle clocks.

Question 2.
We did an activity in the chapter Measurement of Length and Motion’ in the Grade 6 Science textbook Curiosity, where we observed the oscillatory motion of an eraser hung with a thread. Is the pendulum similar to that? (Page 109)
Answer:
A simple pendulum consists of a weight (often called a bob) attached to a fixed point by a string or rod. When it is displaced from its resting position and released, it moves in a repetitive, back- and-forth motion. Eraser experiment demonstrates the same principle. The eraser, like a pendulum bob, oscillates around a fixed point, showcasing periodic motion.

Question 3.
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 races cover the same distance, we can tell who was faster by measuring the time taken.

Question 4.
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 who run at. the same speed have uniform motion, but those who speed up or slow down have non-uniform motion.

NCERT Class 7 Science Chapter 8 Question Answer Measurement of Time and Motion (Exercise)

Let Us Enhance Our Learning (Pages 118-119)

Question 1.
Calculate the speed of a car that travels 150 metres in 10 seconds. Express your answer in km/h.
Answer:
Distance = 150 m
Time taken = 10 s
SPeed = \(\frac{\text { Distance covered }}{\text { Time taken }}\) = \(\frac{150 \mathrm{~m}}{10 \mathrm{~s}}\)
SPeed in km/hr = 15 × \(\frac{18}{5}\) = 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:
Runner 1:
Distance = 400 m,
Time = 50 s
SPeed = \(\frac{\text { Distance covered }}{\text { Time taken }}\) = \(\frac{400 \mathrm{~m}}{50 \mathrm{~s}}\) = 8 m/s

Runner 2:
Distance = 400 m,
Time = 50 s
SPeed = \(\frac{\text { Distance covered }}{\text { Time taken }}\) = \(\frac{400 \mathrm{~m}}{45 \mathrm{~s}}\) = 8.89 m/s
Difference = 8.89 – 8 = 0.89 m/s
Hence, speed of runner 2 is greater by approximately 0.89 m/s.

Question 3.
A train travels at a speed of 25 m/s and covers a distance of360 km. How much time does it take?
Answer:
Speed = 25 m/s
Distance = 360 km = 3,60,000 m
Time taken = \(\frac{\text { Distance }}{\text { Speed }}\) = \(\frac{3,60,0000 \mathrm{~m}}{25 \mathrm{~m} / \mathrm{s}}\)
= 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 = \(\frac{\text { Distance }}{\text { Time }}=\frac{180 \mathrm{~km}}{3 \mathrm{~h}}\) = 60 Km/h
(ii) Speed in m/s= 60 × \(\frac{5}{18}\) = 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 × \(\frac{5}{18}\) = 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: If an objects covers equal distances in equal distance in equal intervals of time, its motion is said to be uniform. A car moving on a straight highway with no traffic is an example of uniform motion.

Non-uniform motion: If an object covers unequal distances in equal interval of time, its motion is said to be non-uniform. A car moving in a traffic is an example of nonuniform 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.

Time (s)	0	10	20	30		50		70
Distance (m)	0	8		24	32	40		56

Answer:
In uniform motion, object covers equal distances in equal intervals of time. Hence, the speed of an object remains constant throughout the motion.

Time (s)	0	10	20	30	40	50	60	70
Distance (m)	0	8	16	24	32	40	48	56

The object covers 8 m in every 10 seconds. Hence, the speed of an object remains constant at 0.8 m/s throughout the 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 = \(\frac{\text { Total distance travelled }}{\text { Total time taken }}\)
= \(\frac{180 \mathrm{~km}}{3 \mathrm{~h}}\) = 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 our daily life, most motions are nonuniform because object do not move at the same speed all the time. Their speed changes due to factors like traffic, rough or uneven roads and other 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.

Time interval (s)	Distance (m)
0-10	6 – 0 = 6
10-20	10 – 6 = 4
20-30	16 – 10 = 6
30-40	21 – 16 = 5
40-50	29 – 21 = 8
50-60	35 – 29 = 6
60-70	42 – 35 = 7
70-80	45 – 42 = 3
80-90	55 – 45 = 10
90-100	60 – 55 = 5

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 = \(\frac{Total distance}{Total time taken}\)
= \(\frac{60}{100}\)
= 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 = \(\frac{\text { Distance }}{\text { Speed }}\) = \(\frac{500}{10}\) = 50 s

Step 2: Time taken to cover the next 500 m
Time = \(\frac{500}{10}\) = 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 = \(\frac{1000}{50}\) = 20 m/s

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

Class 7 Measurement of Time and Motion Question Answer (Activities)

Activity 8.2

Calculating the Time Period of a Simple Pendulum. (Page 109)

Materials Required: A piece of string around 150 cm long, a heavy metal ball with hook/ a stone (bob), a stopwatch/ watch, and a ruler.

Procedure:

1. Tie the bob at one end of the string.
2. Fix the other end of the string to a rigid support such that the length of the string in between support and bob is around 100 cm.
3. Wait for the bob to come to rest. Your pendulum is now ready.

Measurement of Time and Motion

1. Gently hold the bob, move it slightly to one side and release it. ‘
2. Using a watch, measure the time it takes for the pendulum to complete 10 oscillations. Record the time in a Table.
3. Repeat this activity 3-4 times. .
4. Divide the time taken for 10 oscillations by 10 to calculate the time period of your pendulum.

Observations and Records
Table: Time Period of the Simple Pendulum
Length of the Pendulum =100 cm

Time taken for 10 oscillations (seconds)	Time Period (seconds)
20.5	2.05
20.6	2.06.
20.4	2.04
20.6	2.06

It is observed that the time period of the pendulum is almost the same every time.

Activity 8.4

Calculating the Speed of Trains moving out from your nearest Railway Station. (Page 114)

Materials Required: Railway time Table for the trains leaving from your nearest railway station.

Procedure:

1. From the railway time table on the internet identify a train stopping at the railway station nearest to your place of stay.
2. Find out the name of the next station where this train stops. Also, find the distance to that station as given in the timetable.
3. Calculate the time taken by the train to cover the distance till the next station from the difference of starting time from the railway station and reaching time at the next railway station.
4. Calculate the speed of the train between the two stations and record it in a Table.
5. Repeat for 4-5 different types of trains (Passenger/ Express/ Superfast).

Observations and Record:
Table: Finding the speeds of the Trains
Nearest railway station from your place of stay Chandigarh

Name of the Train	Next Station	Distance in km	Time taken by Train in hours	Speed of the train in km/h
Shatabdi Exp.	Ambala	50	0.6	83
Amritsar Exp.	Ludhiana	90	1.8	50
Himalayan Queen	Kalka	30	1.0	30
SMVD Katra Exp.	Jalandhar cantt.	120	1.6	75

Shatabdi Express is the fastest train among these trains with an average speed of 83 km/h to the next station.