Chapter.6. Motion and Time, The Living World, Class – VII, DAV Board, The Best Solutions.

Keywords To Remember

Something To Know

A. Fill in the blanks.

1. An object is said to be at rest if it _________ change its position with time.

Answer – does not

2. The SI unit of time is _________ .

Answer – second

3. A child, sitting in a revolving giant wheel, is an example of a _________ motion.

Answer – circular

4. A car, moving on a busy straight road, is an example of _________ motion.

Answer – non-uniform

5. The speedometer of a motorbike measures its speed in _________.

Answer – kilometres per hour (km/h).

B. Write True or False for the following statements.

1. The speed of a fast moving train is usually measured in metre per hour.

Answer – False

2. The average speed remains constant for an object having a uniform motion.

Answer – True

3. A man walks for 1 minute, at a speed of 1 m/s, along a straight track. The total distance covered by him is 1 m.

Answer – False

4. An object, moving along a straight line, is said to be in uniform motion if it covers regularly increasing distances in equal intervals of time.

Answer – False

5. The time period of a simple pendulum, that takes 42 seconds to complete 20 oscillations, equals 2.1 seconds.

Answer – True

6. The distance-time graph, for a car kept parked on a side road, is a straight line parallel to the time axis.

Answer – True

C. Tick (✓) the correct option.

1. Out of the following, the only correct formula is—

distance x time = speed

distance = speed x time

time = speed/ distance

speed = time/distance

Answer – distance = speed × time

2. A man walks on a straight road from his home to a market 3 km away with a speed of 6 km/h. The time, taken by the man to go from his home to market, equals—

18 minutes

40 minutes

30 minutes

50 minutes

Answer – 30 minutes

3. The odometer of a car reads 57321.0 km when the clock shows the time as 8.30 a.m. The odometer reading changes to 57336.0 km at time 8.50 a.m. The distance, moved by the car, in these 20 minutes, equals—

15 km

26 km

21 km

36 km

Answer – 15 km

4. Out of the following distance-time graphs, the graph that represents a truck at rest, is the graph labelled—

Answer – Graph with horizontal line

5. In the given diagram of a simple pendulum, the time taken by the bob to move from X to Z is ‘t₁‘and from Z to O is ‘t₂‘. The time period of this simple pendulum is-—

Answer – (t₁ + t₂ )

6. The S.I. unit of speed is—

km/minute

km/hour

m/minute

m/second

Answer – m/second

D. Answer the following questions in brief.

1. A boy walks to his school with a constant speed of 4 km/h and reaches there in 30 minutes. Find the distance of the school from his house.

Answer – Distance = Speed × Time = 4 km/h × 0.5 h = 2 km

2. The distance between two stations is 216 km. A bus takes 4 hours to cover this distance. Calculate the average speed of the bus in km/hour.

Answer – Average speed = Total distance ÷ Time = 216 km ÷ 4 h = 54 km/h

3. Two Cars, A and B, (starting, at the same time, from the same point) are moving with average speeds of 40 km/h and 50 km/h, respectively, in the same direction. Find how far will Car B be from Car A after 3 hours.

Answer – Relative speed = 50 − 40 = 10 km/h → Distance = 10 × 3 = 30 km

4.A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. Find the total distance covered by the car in these 30 minutes.

Answer – We are given:

Speed₁ = 40 km/h, Time₁ = 15 minutes = 15/60 = 0.25 hours

Speed₂ = 60 km/h, Time₂ = 15 minutes = 15/60 = 0.25 hours

Now,

Distance₁ = Speed₁ × Time₁ = 40 × 0.25 = 10 km

Distance₂ = Speed₂ × Time₂ = 60 × 0.25 = 15 km

Total distance covered = Distance₁ + Distance₂ = 10 km + 15 km = 25 km
5.Define the term ‘Periodic motion. Give two examples of periodic motions that can be used to measure time.

Answer – Periodic motion is the motion that repeats itself after equal intervals of time.

Examples:

The swinging of a simple pendulum – It completes each oscillation in a fixed interval and is used in pendulum clocks.

The revolution of the Earth around the Sun – It is used to measure a year.

These periodic motions help in timekeeping because they are regular and repeat consistently.

6. Distinguish between uniform and non-uniform motion. Give one example of each.

Answer – Uniform motion: Equal distances in equal time intervals (e.g., car on highway).

Non-uniform motion: Unequal distances in equal time intervals (e.g., walking in a crowded street).

7. Draw the shape of distance-time graph for:

(a) a man, waiting for a bus, standing at one point, on a bus-stand.

Answer – Horizontal line parallel to time axis.

(b) a man, walking on a level, straight and narrow road, with a constant speed.

Answer – Straight line with positive slope.

E. Answer the following questions

1. A farmer moves along the boundary of a rectangular field ABCD as shown in the figure. He takes 4 minutes to travel across each side.

Is the motion of this farmer uniform or non-uniform? Find his average speed over one complete round of the field.

Answer – Given:

• The field is rectangular:
  Length = 80 m, Breadth = 40 m
• Time taken to travel each side = 4 minutes
• There are 4 sides, so total time for one round = 4 sides × 4 min = 16 minutes

1. Is the motion of the farmer uniform or non-uniform?

• Uniform motion means covering equal distances in equal intervals of time in the same direction (constant velocity).
• Here, although he takes the same time for each side, the direction changes at each corner.

Answer: The motion is non-uniform because the direction keeps changing.

2. Total Distance Travelled:

Since the farmer walks around the rectangle once:

• Total distance = AB + BC + CD + DA
  = 80 m + 40 m + 80 m + 40 m = 240 meters

3. Total Time Taken:

As calculated, time = 4 min × 4 sides = 16 minutes = 960 seconds

4. Average Speed:

Average Speed=Total Time/Total Distance​=960s/240m​=0.25m/s

Final Answers:

• The motion is non-uniform because the direction changes at each corner.
• Average speed = 0.25 m/s

2. During rainy season, Shivam noted that the thundering sound of clouds was heard 6 seconds after the lightening was seen by him. If speed of sound in air is 340 m/s, find the distance of the point where the thundering sound was produced.

Answer – Distance = Speed × Time = 340 m/s × 6 s = 2040 m

3. (a) How can we make a simple pendulum?

Answer – A simple pendulum is made by tying a small ball (bob) to a string fixed at one end.

(b) A simple pendulum takes 10 seconds to complete 5 oscillations. Find the time period of this pendulum.

Answer – Time period = Total time ÷ No. of oscillations = 10 ÷ 5 = 2 seconds

4. Carefully examine the data given below for motion of two different objects A and B. State whether the motion of these two objects is uniform or non- uniform.

Time —> 7.00 a.m. 7.30 a.m. 7.45 a.m. 8.00 a.m. 8.15 a.m. 8.30 a.m.

Total distance covered by A (in metres at the given time) —> 0 20 30 40 50 60

Distance covered by B (in metres at the given time) —> 0 10 24 35 38 43

Answer –

(a) Who is moving with uniform speed?

To check this, observe the distance covered per time interval:

For A (every 15 min = 0.25 h):

• 7.00–7.30 → 20 m
• 7.30–7.45 → 10 m
• 7.45–8.00 → 10 m
• 8.00–8.15 → 10 m
• 8.15–8.30 → 10 m

From 7.30 a.m. onwards, A is moving 10 m every 15 minutes, which is uniform speed.

A is moving with uniform speed.

For B:

• 7.00–7.30 → 10 m
• 7.30–7.45 → 14 m
• 7.45–8.00 → 11 m
• 8.00–8.15 → 3 m
• 8.15–8.30 → 5 m

The distances are not constant, hence:

B is moving with non-uniform speed.

(b) Who covers more distance in 1 hour and by how much?

From 7.30 a.m. to 8.30 a.m. (1 hour):

• A: 60 – 20 = 40 meters
• B: 43 – 10 = 33 meters

 A covers more distance.

Difference = 40 – 33 = 7 meters

A covers 7 meters more than B in 1 hour.

Final Answers:

(a) A is moving with uniform speed, B is not.
(b) A covers more distance than B in 1 hour by 7 meters.

5. Observe the graph given here. From the graph, find (i) the values of distances ‘P’ and ‘Q’ in ‘m’ and (ii) the value of time ‘R’ in ‘seconds’.

Distance (m) -> 0 ‘P’ 6 9 ‘Q’ 15

Time (s) —> 0 4 8 ‘R’ 16 20

Answer –

Now fill the missing values:

From the table:

• At time 4 s, distance = P = 3 m
• At time 16 s, distance = Q = 12 m
• At distance 9 m, time = R = 12 s

Final Table:

Value Based Question

In the science class, Drishti observed a video showing the working of a pendulum wall clock. She noted that a slight change in the initial displacement of the (bob) did not affect the time-period of the pendulum. When she discussed her observation with her grandfather, he told her that we must also not let the effects of small disturbances to change the daily routine and the values of our life.

1. State any four values that we should maintain in our life.

Answer- Punctuality

Patience

Consistency

Discipline

2. Design an activity to show that a slight change, in the initial displacement of the bob, does not affect the time period of a simple pendulum.

Answer- Activity:

Make a simple pendulum with string and bob.

Displace bob slightly and release it.

Use stopwatch to measure time for 10 oscillations.

Repeat with slightly larger displacement.

Divide time by 10 to get time period.

Observation: Time period remains the same.

Something To Do

1. The following figure shows the distance-time graph for two students A and B who start from their school and reach their respective homes. Examine it carefully and answer the following questions:

(a) Who starts first from the school?

From the graph:

• The line for B starts from the origin before the line for A.
• Therefore, B starts first from the school.

Answer: B

(b) Who reaches home first?

From the graph:

• The line for A reaches its maximum distance (home) earlier on the time axis than B.
• Hence, A reaches home first.

Answer: A

(c) Who covers more distance?

From the graph:

• A’s home is at a greater distance from the school compared to B’s (A’s line ends higher on the y-axis).
• So, A covers more distance.

Answer: A

(d) Whose average speed is more?

Average speed = Total distance/Total time

A covers more distance in less time.

• Therefore, A’s average speed is greater.

Answer: A

2. Assume that the distance between Bengaluru and Delhi is 1200 km by air and 1500 km by train. A person takes 2 hours to reach there by air but needs 25 hours to reach there by train. Find the average speed in both the cases. Repeat this exercise by collecting data for different cities.

Answer- By air: Speed = 1200 km ÷ 2 h = 600 km/h

By train: Speed = 1500 km ÷ 25 h = 60 km/h

3. Draw a long straight line on the ground. Mark points at distances 10 m, 20 m, 30 m and so on. Compare your speed of walking with that of your friends. Measure the time taken to cover a known distance using a stop watch. Find out who amongst you is the fastest. Represent your results in the form of a table. Draw a bar-graph to show the speeds of different students. Also draw ‘distance-time’ graphs for each student.

Answer-

4. Collect information about the time of starting from the home and the time of arrival at school for your classmates. Record it in the following table. Use this data to calculate the average speed of each student. (For distance covered use the shortest distance from your classmates’ home to school as measured on an accurate local map.

 Answer –

Additional Questions And Answers – 01

Fill in the blanks (with answers)

1. The basic unit of speed in the SI system is __________.
   Answer: metre/second (m/s)
2. A car moving with unequal distances in equal intervals of time is said to be in __________ motion.
   Answer: non-uniform
3. The time taken to complete one oscillation is called the __________ of a pendulum.
   Answer: time period
4. The distance travelled divided by the time taken gives the __________ of an object.
   Answer: speed
5. A distance-time graph of an object at rest is a line __________ to the time axis.
   Answer: parallel
6. The longer hand of a clock shows the __________.
   Answer: minutes
7. Speed is a __________ quantity as it has only magnitude and no direction.
   Answer: scalar
8. The time shown by a clock is measured in __________.
   Answer: hours, minutes and seconds

Multiple Choice Questions (MCQs)

1. The speed of an object is calculated by:
2. a) Time ÷ Distance
3. b) Distance × Time
4. c) Distance ÷ Time
5. d) Speed × Distance
   Answer: c) Distance ÷ Time
6. Which of the following instruments measures time?
7. a) Thermometer
8. b) Barometer
9. c) Stopwatch
10. d) Speedometer
    Answer: c) Stopwatch
11. Which motion is shown by the second hand of a clock?
12. a) Rectilinear
13. b) Oscillatory
14. c) Circular
15. d) Periodic
    Answer: c) Circular
16. An example of periodic motion is:
17. a) A car moving on a road
18. b) A ball thrown up
19. c) The earth revolving around the sun
20. d) A running athlete
    Answer: c) The earth revolving around the sun
21. The speed of sound in air is approximately:
22. a) 300 m/s
23. b) 340 m/s
24. c) 400 m/s
25. d) 280 m/s
    Answer: b) 340 m/s

🅒 True or False

1. A distance-time graph of a body in uniform motion is a straight line.
   Answer: True
2. A pendulum shows rectilinear motion.
   Answer: False
3. The more the speed of an object, the less distance it travels in a given time.
   Answer: False
4. A bus taking turns on a hilly road is an example of non-uniform motion.
   Answer: True
5. The odometer measures the speed of the vehicle.
   Answer: False

Short Answer Questions

1. Define average speed.
   Answer: Average speed is the total distance travelled divided by the total time taken.
2. What is meant by oscillatory motion?
   Answer: Motion that repeats itself in equal intervals of time, like a pendulum, is called oscillatory motion.
3. What is a simple pendulum?
   Answer: A simple pendulum consists of a string with a bob attached at one end and fixed at the other end, which swings freely.
4. How can we measure the time taken by an object to move a certain distance?
   Answer: By using a stopwatch to note the time taken and a scale to measure the distance covered.
5. What does the slope of a distance-time graph indicate?
   Answer: It indicates the speed of the object.

Competency-Based Questions (Assertion and Reasoning)

1. Assertion: A clock shows periodic motion.
   Reason: Periodic motion repeats after a fixed interval.
2. a) Both A and R are true, and R is the correct explanation of A.
3. b) Both A and R are true, but R is not the correct explanation of A.
4. c) A is true, R is false.
5. d) A is false, R is true.
   Answer: a) Both A and R are true, and R is the correct explanation of A.
6. Assertion: The distance-time graph of an object at rest is a curved line.
   Reason: A curved line in a distance-time graph indicates a change in speed.
   Answer: d) A is false, R is true.
7. Assertion: A speedometer measures the distance travelled.
   Reason: Odometer is used to measure the distance.
   Answer: c) A is false, R is true.

High Order Thinking Skill (HOTS) Questions

1. Why do we prefer average speed to measure motion over a long journey?
   Answer: Because during a long journey, speed may not be constant due to traffic, signals, and road conditions, hence average speed gives a more accurate representation of the entire trip.
2. A cyclist covers 10 km in 25 minutes and 5 km in the next 15 minutes. Is the motion uniform or non-uniform? Justify.
   Answer: The motion is non-uniform as the cyclist covers different distances in equal intervals of time, indicating varying speed.
3. Two students record their speeds walking to school over the same distance but at different times. One walks faster but starts later and reaches earlier. How can this be interpreted on a distance-time graph?
   Answer: The graph of the faster student will have a steeper slope, indicating higher speed and less time taken for the same distance.

Long Answer Questions (50–60 words)

1. Explain how a distance-time graph helps in understanding the motion of an object.
   Answer: A distance-time graph shows how distance changes with time. A straight-line graph indicates uniform motion, while a curved line shows non-uniform motion. A horizontal line parallel to the time axis shows the object is at rest. It visually represents speed and motion patterns effectively.
2. Describe how you would calculate the average speed of a car using odometer and clock readings.
   Answer: Note the initial odometer reading and time. After a known time, take the final reading. Subtract to get distance travelled. Divide this by the time taken. For example, if a car travels 30 km in 1 hour, average speed = 30 km ÷ 1 hr = 30 km/h.

Additional Questions And Answers – 02

Fill in the Blanks

1. An object is said to be in ________ if its position changes with respect to its surroundings over time.

Answer: Motion

2. Motion along a straight line is also called ________ motion.

Answer: Rectilinear

3. Speed is defined as the distance covered per ________ time.

Answer: Unit

4. The SI unit of speed is ________ per second.

Answer: Metre

5. An object moving along a straight path with constant speed is said to be in ________ motion.

Answer: Uniform

6. The time taken for one complete oscillation of a pendulum is called its ________ period.

Answer: Time

7. A ________ pendulum consists of a metal bob attached to a taut string fixed at one end.

Answer: Simple

8. The device in a car that measures the distance covered is called an ________.

Answer: Odometer

9. In a distance-time graph, the motion of an object with constant speed is represented by a ________ line.

Answer: Straight

10. The average speed of an object is calculated as total distance divided by total ________ taken.

Answer: Time

Multiple Choice Questions (MCQs)

1. When is an object said to be at rest?
2. a) Its position changes with time
3. b) Its position does not change with time
4. c) It moves in a circular path
5. d) It oscillates periodically

Answer: b) Its position does not change with time

2. What type of motion is the straight march-past of soldiers in a parade?
3. a) Circular motion
4. b) Oscillatory motion
5. c) Rectilinear motion
6. d) Rotational motion

Answer: c) Rectilinear motion

3. What is the average speed of a car that travels 440 km in 8 hours?
4. a) 50 km/h
5. b) 55 km/h
6. c) 60 km/h
7. d) 45 km/h

Answer: b) 55 km/h

4. Which of the following is an example of uniform motion?
5. a) A car traveling 30 km each hour for three hours on a straight road
6. b) A car traveling 20 km in the first hour and 40 km in the second hour
7. c) A car moving in a circular path at constant speed
8. d) A car stopping at traffic lights

Answer: a) A car traveling 30 km each hour for three hours on a straight road

5. What is the time period of a pendulum?
6. a) The time taken for 10 oscillations
7. b) The time taken for one complete oscillation
8. c) The length of the pendulum thread
9. d) The speed of the pendulum bob

Answer: b) The time taken for one complete oscillation

6. What does the slope of a distance-time graph represent for an object in uniform motion?
7. a) Time
8. b) Distance
9. c) Speed
10. d) Acceleration

Answer: c) Speed

7. Which device measures the instantaneous speed of a vehicle?
8. a) Odometer
9. b) Speedometer
10. c) Stopwatch
11. d) Pendulum clock

Answer: b) Speedometer

8. What is the speed of the fastest animal, the cheetah?
9. a) 200 km/h
10. b) 115 km/h
11. c) 340 m/s
12. d) 30 km/s

Answer: b) 115 km/h

9. How long will a bus take to travel 250 km at an average speed of 50 km/h?
10. a) 4 hours
11. b) 5 hours
12. c) 6 hours
13. d) 3 hours

Answer: b) 5 hours

10. What type of motion does a simple pendulum exhibit?
11. a) Linear motion
12. b) Circular motion
13. c) Oscillatory motion
14. d) Rotational motion

Answer: c) Oscillatory motion

True/False Questions

1. Motion is absolute and does not depend on the observer.

Answer: False (Motion is relative and depends on the observer)

2. A car covering equal distances in equal intervals of time is in uniform motion.

Answer: True

3. The SI unit of speed is kilometre per hour.

Answer: False (The SI unit of speed is metre per second)

4. The motion of an object in a circular path can be considered uniform motion.

Answer: False (Uniform motion occurs only along a straight path)

5. A simple pendulum’s time period depends on the length of its thread.

Answer: True

6. The speed of light in air is 340 m/s.

Answer: False (The speed of light in air is 3 x 10^8 m/s)

7. A distance-time graph for uniform motion is a straight line.

Answer: True

8. The odometer of a vehicle measures its speed.

Answer: False (The odometer measures distance; the speedometer measures speed)

9. Periodic events, like sunrise and sunset, were used in ancient times to measure time.

Answer: True

10. Non-uniform motion occurs when an object covers equal distances in equal intervals of time.

Answer: False (Non-uniform motion occurs when distances covered in equal intervals are unequal)

Short Questions and Answers

1. What is motion?

Answer: Motion is the change in an object’s position with respect to its surroundings over time.

2. How is an object at rest defined?

Answer: An object is at rest if its position does not change with respect to its surroundings over time.

3. What is rectilinear motion?

Answer: Rectilinear motion is the motion of an object along a straight line, such as a train on a straight track.

4. How is speed calculated?

Answer: Speed is calculated as the distance covered per unit time, using the formula: speed = distance / time.

5. What is uniform motion?

Answer: Uniform motion occurs when an object moves along a straight path and covers equal distances in equal intervals of time.

6. What is the role of a speedometer in a vehicle?

Answer: A speedometer measures the instantaneous speed of a vehicle, displaying it in km/h.

7. What is a simple pendulum?

Answer: A simple pendulum is a metal bob attached to a taut string fixed at one end, which oscillates when displaced.

8. How is the time period of a pendulum measured?

Answer: The time period is measured by recording the time for a set number of oscillations (e.g., 10) and dividing by the number of oscillations.

9. What does a distance-time graph represent?

Answer: A distance-time graph represents the motion of an object, with distance on the y-axis and time on the x-axis.

10. What is non-uniform motion?

Answer: Non-uniform motion occurs when an object covers unequal distances in equal intervals of time or does not move in a straight path.

 Competency-Based Questions (Reasoning and Assertion)

1. Assertion (A): A car covering 30 km each hour for three hours is in uniform motion. Reason (R): Uniform motion occurs when an object covers equal distances in equal intervals of time along a straight path.
2. a) Both A and R are true, and R is the correct explanation of A.
3. b) Both A and R are true, but R is not the correct explanation of A.
4. c) A is true, but R is false.
5. d) A is false, but R is true.

Answer: a) Both A and R are true, and R is the correct explanation of A.

2. Assertion (A): The motion of a car in a circular path is uniform motion. Reason (R): Uniform motion requires the object to move along a straight path.
3. a) Both A and R are true, and R is the correct explanation of A.
4. b) Both A and R are true, but R is not the correct explanation of A.
5. c) A is true, but R is false.
6. d) A is false, but R is true.

Answer: d) A is false, but R is true.

3. Assertion (A): Motion is relative. Reason (R): An object can be at rest for one observer and in motion for another.
4. a) Both A and R are true, and R is the correct explanation of A.
5. b) Both A and R are true, but R is not the correct explanation of A.
6. c) A is true, but R is false.
7. d) A is false, but R is true.

Answer: a) Both A and R are true, and R is the correct explanation of A.

4. Assertion (A): A pendulum’s time period changes with its initial displacement. Reason (R): The time period of a pendulum depends on its length, not its displacement.
5. a) Both A and R are true, and R is the correct explanation of A.
6. b) Both A and R are true, but R is not the correct explanation of A.
7. c) A is true, but R is false.
8. d) A is false, but R is true.

Answer: d) A is false, but R is true.

5. Assertion (A): The speed of a cheetah is faster than the speed of sound in air. Reason (R): The speed of a cheetah is 115 km/h, while the speed of sound in air is 340 m/s.
6. a) Both A and R are true, and R is the correct explanation of A.
7. b) Both A and R are true, but R is not the correct explanation of A.
8. c) A is true, but R is false.
9. d) A is false, but R is true.

Answer: d) A is false, but R is true. (340 m/s = 1224 km/h, much faster than 115 km/h.)

 High Order Thinking Skill (HOTS) Questions and Answers

1. Why is motion considered relative?

Answer: Motion is relative because an object’s state of motion or rest depends on the observer. For example, passengers in a moving train are at rest relative to each other but in motion relative to someone on the platform.

2. How does a distance-time graph help in understanding the motion of an object?

Answer: A distance-time graph shows how distance changes with time. For uniform motion, it’s a straight line, where the slope represents speed. A curved line indicates non-uniform motion, helping to analyze how speed varies over time.

3. Why does the time period of a simple pendulum remain constant for a given length?

Answer: The time period of a simple pendulum depends on its length and gravity, not on its mass or displacement. For a fixed length, the time taken for one oscillation remains constant, as discovered by Galileo.

4. How can you determine if an object’s motion is uniform or non-uniform using data?

Answer: If an object covers equal distances in equal time intervals along a straight path, its motion is uniform, like a car covering 30 km each hour. If distances vary, like a bus covering 4 km, 2 km, and 3 km in 5-minute intervals, it’s non-uniform.

5. Why are stopwatches used instead of regular clocks for measuring short time intervals?

Answer: Stopwatches can be started and stopped precisely, making them ideal for measuring short intervals, like an athlete’s 100 m run time. Regular clocks run continuously and cannot accurately measure such brief, specific durations.

 Long Questions and Answers (50-60 words)

1. Explain the difference between uniform and non-uniform motion with examples.

Answer: Uniform motion occurs when an object covers equal distances in equal intervals along a straight path, like a car traveling 30 km each hour. Non-uniform motion involves unequal distances in equal intervals or a non-straight path, such as a car covering 20 km in the first hour and 40 km in the second.

2. Describe how the time period of a simple pendulum is measured experimentally.

Answer: Set up a simple pendulum with a fixed length, displace the bob slightly, and let it oscillate. Start a stopwatch when the bob is at an extreme position, record the time for 10 oscillations, and stop the watch. Divide the total time by 10 to find the time period in seconds.

3. How is the average speed of a vehicle calculated? Provide an example.

Answer: Average speed is calculated as total distance divided by total time. For example, if a car travels 400 km in 8 hours, its average speed is 400 km ÷ 8 h = 50 km/h. This accounts for variations in speed during the journey, including stops.

4. What is a distance-time graph, and how does it represent uniform motion?

Answer: A distance-time graph plots distance on the y-axis and time on the x-axis. For uniform motion, it’s a straight line inclined to the time axis, indicating constant speed. The slope of the line represents the speed, showing equal distances covered in equal time intervals.

5. How did ancient people measure time using natural events?

Answer: Ancient people measured time using periodic natural events. A day was the interval between two sunrises, a month was from one new moon to the next, and a year was the time for Earth to complete one revolution around the sun, based on seasonal changes.