Science Class 7 CBQ of Measurement of Time and Motion (Remarkable Breakthrough)

Science Class 7 CBQ of Measurement of Time and Motion

Science Class 7 CBQ of Measurement of Time and Motion

Section A: Multiple Choice Questions

1. What unit is used to measure time in the SI system?

a) Minute
b) Hour
c) Second
d) Millisecond

2. Name the ancient device that measured time by the flow of sand between two connected bulbs.

a) Sundial
b) Water clock
c) Hourglass
d) Candle clock

3. In 1656, who developed the first pendulum clock?

a) Galileo Galilei
b) Aryabhata
c) Christiaan Huygens
d) Varahamihira

4. The duration a pendulum takes to finish one full swing is known as its:

a) Frequency
b) Speed
c) Time period
d) Amplitude

5. Which instrument in a vehicle measures the distance travelled in kilometres?

a) Speedometer
b) Odometer
c) Thermometer
d) Barometer

6. A simple pendulum’s time period depends on:

a) Mass of the bob
b) Length of the string
c) Colour of the bob
d) Material of the thread

7. The Samrat Yantra in Jaipur is a type of:

a) Water clock
b) Pendulum clock
c) Sundial
d) Candle clock

8. If a car covers 100 metres in 20 seconds, its speed is:

a) 5 m/s
b) 10 m/s
c) 2 m/s
d) 20 m/s

9. A train moving at a constant speed on a straight track is an example of:

a) non-uniform linear motion
b) Circular motion
c) Uniform linear motion
d) Oscillatory motion

10. In ancient India, the sinking bowl water clock was also known as:

a) Samrat Yantra
b) Ghatika-yantra
c) Braille watch
d) Quartz clock

Science Class 7 CBQ of Measurement of Time and Motion

Which of the following correctly pairs an ancient timekeeping device with its operational principle?

A) Sundial – Flow of sand between two glass bulbs

B) Ghatika-yantra – Position of a shadow cast by a vertical stick

C) Candle Clock – Consumption of fuel marked with time passages

D) Hourglass – Sinking of a floating bowl with a fine bottom hole

The historical stone sundial known as the Samrat Yantra is located at Jantar Mantar in which city?

A) Delhi

B) Jaipur

C) Udaipur

D) Jodhpur

Why were the early water clocks that relied on water flowing out of a vessel considered inaccurate over long intervals?

A) Water evaporated too quickly in the sun.

B) The hole at the bottom would widen over time.

C) The flow rate decreased as the water level dropped.

D) Water density changed based on room temperature.

Who invented and patented the first mechanical pendulum clock?

A) Galileo Galilei

B) Christiaan Huygens

C) Kautilya

D) Varahamihira

When a simple pendulum is at rest, hanging straight down, it is positioned at its:

A) Mean position

B) Extreme position A

C) Extreme position B

D) Amplitude position

A pendulum is said to complete exactly one full oscillation when its bob travels:

A) From its mean position O to extreme position A and stops.

B) From extreme position A to extreme position B only.

C) From mean position O to extreme A, then to extreme B, and back to O.

D) From mean position O to extreme A and back to O.

What is the standard SI unit of time and its officially recognized symbol?

A) Minute (min)

B) Second (sec)

C) Second (s)

D) Hour (h)

According to the text’s formatting rules for scientific units, which of the following expressions is written correctly?

A) 15 sec

B) 4 hrs

C) 20 s.

D) 10 h

Which automobile instrument measures and displays speed in km/h?

A) Odometer

B) Speedometer

C) Chronometer

D) Tachometer

An object moving along a straight-line path with a completely unchanging, constant speed is executing:

A) Non-uniform linear motion

B) Uniform linear motion

C) Oscillatory periodic motion

D) Non-uniform periodic motion

Science Class 7 CBQ of Measurement of Time and Motion

Section B: Higher Order Thinking (HOT) MCQs

1. If a pendulum takes 30 seconds to complete 20 oscillations, what is its time period?
a) 0.67 s
b) 1.5 s
c) 2.0 s
d) 0.5 s

2. Two pendulums have lengths L and 4L. How will their time periods compare at the same location?
a) The time period of a longer pendulum is twice that of a shorter one
b) Time period of longer pendulum is four times
c) Both have same time period
d) The time period of a shorter pendulum is twice that of a longer one.

3. A water clock based on outflow becomes less accurate as water level drops. Why?
a) Water evaporates faster
b) Flow rate decreases with lower pressure
c) The vessel expands
d) Colour of water fades

4. If a train’s speed is 90 km/h, how many metres does it cover in 10 seconds?
a) 250 m
b) 150 m
c) 900 m
d) 25 m

5. A runner finishes 100 m in 12 s. Another finishes 200 m in 24 s. Who is faster?
a) First runner
b) Second runner
c) Both have same speed
d) Cannot be determined

6. Why did ancient water clocks with floating bowls improve accuracy over outflow clocks?
a) They used sand instead of water
b) Flow rate remained more constant
c) They were larger in size
d) They used mercury

7. A pendulum clock gains 10 seconds per day. If its length is slightly increased, what will happen?
a) Time period decreases, clock gains more
b) Time period increases, clock loses time
c) No change
d) Pendulum stops

8. If an atomic clock loses 1 second in 1 million years, how many seconds would it lose in 10 million years?
a) 1
b) 10
c) 100
d) 0.1

9. In a 100 m race, two runners finish at the same time but one had a slower start. What can be concluded?
a) Both had same average speed
b) Both had same instantaneous speed at finish
c) One had higher top speed
d) Both ran with uniform motion

10. Why can’t a sundial be used accurately at night or on a cloudy day?
a) It uses water flow
b) It depends on the Sun’s shadow
c) It requires electricity
d) It works only indoors

Science Class 7 CBQ of Measurement of Time and Motion

Swati rides her bicycle to school and covers a total distance of 3.6 km in 15 minutes. What is her cycling speed expressed in meters per second (m/s)?

A) 0.24 m/s

B) 4 m/s

C) 14.4 m/s

D) 240 m/s

A high-speed train travels at a constant speed of 90 km/h. How many hours would it take to travel the 360 km distance between the two cities?

A) 0.25 hours

B) 2.5 hours

C) 4 hours

D) 32,400 hours

Two pendulums are made in an identical location. Both have a string length of 100 cm, but Pendulum A’s bob weighs 50 g and Pendulum B’s weighs 150 g. Which prediction about their time periods is correct?

A) Pendulum B will have a significantly longer time period because it is heavier.

B) Pendulum A will have a longer time period because lighter masses swing faster.

C) Both pendulums will have the exact same time period.

D) The time periods cannot be compared without knowing the width of the swing.

Imagine you are Galileo. While trying to verify the time period of a newly designed long-string pendulum without any mechanical clock available, which resource mentioned in the text would be most reliable to measure short intervals?

A) The Moon’s varying appearances throughout the month.

B) Your own resting pulse beat

C) The rising of the Sun

D) The changing seasonal temperature

Why does the Samrat Yantra stone sundial require a calculation correction to determine Indian Standard Time (IST)?

A) It loses up to 10 seconds every single day.

B) It natively measures local solar time based on its specific geographic longitude.

C) The shadow moves too quickly at 1 mm per second to be naturally stable.

D) It only operates accurately during seasonal equinoxes.

If a car goes 180 km in 3 hours and continues at the same average speed, what total distance will it cover in 4 hours?

A) 60 km

B) 220 km

C) 240 km

D) 720 km

The maximum speed of a galloping horse is roughly 18 m/s, and a local express train moves at 72 km/h. Identify the faster option and determine the speed gap between them.

A) The horse is faster than the train.

B) The train is faster than the horse.

C) The horse and the train are moving at the exact same speed.

D) The train is exactly twice as fast as the horse.

In modern electronic applications, devices such as smartphones and central computer processors read, route, and execute internal signals at speeds measured in microseconds. A microsecond is defined as:

A) One-hundredth of a second

B) One-thousandth of a second

C) One-millionth of a second

D) One-billionth of a second

Why is the concept of “uniform linear motion” described as an idealization in everyday human life?

A) Most objects naturally travel along curved pathways instead of straight lines.

B) Friction, traffic, and environmental constraints cause real-world objects to constantly change speed.

C) Modern atomic clocks are too fast to measure true uniform states.

D) Human perception cannot accurately observe a constant velocity.

A vehicle moves along a straight road covering a total distance of 2 km (2000 m). In the first 500 m, it travels at a speed of 10 m/s. In the next 500 m, it travels at 5 m/s. If the entire 2 km journey must be completed in exactly 200 seconds, at what constant speed must the vehicle travel for the remaining 1000 m?

A) 5 m/s

B) 10 m/s

C) 20 m/s

D) 25 m/s

Science Class 7 CBQ of Measurement of Time and Motion

Section C: Data Analysis-Based MCQs

A student measures the time for 10 oscillations of a pendulum three times:

Trial	Time for 10 oscillations (s)
1	15.0
2	15.2
3	14.8

What is the average time period of the pendulum?

A) 1.50 s
B) 1.52 s
C) 1.48 s
D) 1.55 s

Four different pendulums have the following lengths and time periods (measured experimentally):

Pendulum	Length (cm)	Time period (s)
A	25	1.00
B	50	1.41
C	100	2.00
D	200	2.83

When you increase the length from 50 cm to 100 cm, roughly how many times does the time period grow?

A) 1.41
B) 2.00
C) 1.00
D) 0.71

The table below shows the distance covered by a vehicle every 10 seconds:

Time (s)	Distance (m)
0–10	50
10–20	50
20–30	50
30–40	50

Calculate the vehicle’s speed using meters per second as the unit.

A) 5 m/s
B) 10 m/s
C) 20 m/s
D) 50 m/s

An athlete runs 400 m in 50 seconds. Another runs 200 m in 25 seconds. What can be concluded about their average speeds?

A) First athlete is faster
B) Second athlete is faster
C) Both have the same average speed
D) Cannot be compared

A train travels between three stations. Data:

Station	Distance from start (km)	Arrival time
A	0	10:00 AM
B	90	11:00 AM
C	180	12:30 PM

What is the average speed of the train from A to C?

A) 60 km/h
B) 72 km/h
C) 90 km/h
D) 120 km/h

The distance covered by an object in successive 5-second intervals is:

Interval	Distance (m)
0–5 s	10
5–10 s	15
10–15 s	20
15–20 s	25

What is the average speed over the full 20 seconds?

A) 3.5 m/s
B) 4.0 m/s
C) 4.5 m/s
D) 5.0 m/s

A pendulum’s time period is measured 5 times at the same length:

Reading	Time period (s)
1	2.01
2	1.99
3	2.00
4	2.02
5	1.98

Determine the most exact value for the time period.

A) 2.00 s
B) 2.01 s
C) 1.99 s
D) 2.02 s

In a race, three runners cover 100 m. Their finish times are:

Runner	Time (s)
X	12.5
Y	13.0
Z	12.0

If they run the same distance again at the same average speed, how far behind the finish line will Y be when Z finishes?

A) 0 m
B) ~4.2 m
C) ~8.3 m
D) Cannot be determined

A student measures the time period of pendulums with different bob masses (length fixed at 100 cm):

Mass (g)	Time period (s)
50	2.01
100	2.00
150	2.02
200	1.99

What conclusion is supported by the data?

A) Time period increases with mass
B) Time period decreases with mass
C) Time period is independent of mass
D) Time period depends only on mass

The table below shows the time taken for a water clock to empty from different starting water levels:

Starting level (cm)	Time to empty (s)
10	30
20	85
30	155

If the level is 40 cm, the time to empty is most likely:

A) ~120 s
B) ~200 s
C) ~240 s
D) ~310 s

Use the training data matrix below to answer Questions 11 to 15:

The tracking table captures the positions and incremental distances covered by two different experimental trains (Train X and Train Y) inside equal checking windows of 10 minutes.

Time (AM)	Train X: Position (km)	Train X: Distance travelled during a specific time period (km)	Train Y: Position (km)	Train Y: Distance travelled during a specific time period (km)
10:00	0	0	0	0
10:10	20	20	20	20
10:20	40	20	35	15
10:30	60	20	50	15
10:40	80	20	75	25
10:50	100	20	95	20
11:00	120	20	120	25

Science Class 7 CBQ of Measurement of Time and Motion

how much distance does Train X cover between 10:20 AM and 10:40 AM?
a) 20 km
b) 30 km
c) 40 km
d) 10 km
which train shows non-uniform motion?
a) Train X
b) Train Y
c) Both
d) Neither
Based on the calculated dataset patterns, which train is verified to be in uniform linear motion?

A) Train Y, because its position keeps increasing continuously over time.

B) Train X, because it covers an identical, constant distance of 20 km during every single 10-minute time interval.

C) Both Train X and Train Y are in uniform linear motion because they start and end at the same positions.

D) Neither train, because their speeds fluctuate wildly between 10:10 AM and 10:40 AM.

What is the calculated average hourly speed of Train X across the entire 10:00 AM to 11:00 AM test window?

A) 20 km/h

B) 60 km/h

C) 120 km/h

D) 240 km/h

During which 10‑minute data collection period did Train Y show its slowest performance?

A) 10:00 AM – 10:10 AM

B) 10:10 AM – 10:30 AM

C) 10:30 AM – 10:40 AM

D) 10:50 AM – 11:00 AM

A student investigates how the time period of a simple pendulum changes with length. She records the following data:

Length (cm)	Time for 10 oscillations (s)	Time period (s)
40.0	12.6	1.26
90.0	19.0	1.90
160.0	25.2	2.52

She then plots a graph of time period (s) vs. square root of length (√cm). The calculated values are:

Length (cm)	√Length (√cm)	Time period (s)
40.0	6.32	1.26
90.0	9.49	1.90
160.0	12.65	2.52

Based on this pattern, approximately what would be the time period for a pendulum with a length of 250 cm?

A) 2.80 s
B) 3.15 s
C) 3.50 s
D) 4.00 s

Use the incomplete uniform motion tracking dataset below to answer Questions 17, 18, and 19:

An object is observed to be in ideal uniform linear motion along a test track.

Time (seconds)	0	10	20	30	50	70
Distance (meters)	0	8	[Gap 1]	24	40	[Gap 2]

What is the constant operational speed of this uniform object?

A) 0.8 m/s

B) 1.2 m/s

C) 2.4 m/s

D) 8.0 m/s

What is the exact numerical value required to fill [Gap 1] at the 20‑second tracking mark?

A) 12 meters

B) 16 meters

C) 18 meters

D) 20 meters

What is the correct mathematical value needed to fill [Gap 2] at the 70-second tracking mark?

A) 48 meters

B) 52 meters

C) 56 meters

D) 64 meters

Refer to the table of non-uniform performance below to answer Questions 20 through 23:

A research vehicle’s variable position metrics are recorded across 100 seconds.

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

Based on the distance values over equal 10-second intervals (e.g., 6m, 4m, 6m, 5m…), the speed of this object is classified as:

A) Ideal Uniform

B) Non-Uniform

C) Exponentially Accelerating

D) Constant Periodic

What is the total distance covered by the vehicle at the end of the 100-second testing window?

A) 6 meters

B) 45 meters

C) 60 meters

D) 100 meters

Calculate the true overall average speed of the vehicle across the entire 100-second run.

A) 0.6 m/s

B) 1.0 m/s

C) 6.0 m/s

D) 60 m/s

Between which two checking intervals did the vehicle show its lowest incremental movement (covering only 3 meters)?

A) 10 s to 20 s

B) 30 s to 40 s

C) 70 s to 80 s

D) 90 s to 100 s

Science Class 7 CBQ of Measurement of Time and Motion

Section D: Assertion-Reason Based Questions

Instructions: Choose the correct option:

Both A and R are factually correct, and R provides the precise logical explanation for A.
A is true and R is also true, but R does not logically justify or clarify A.
Assertion A holds true; however, the reason given in R is factually incorrect.
Assertion A is not valid, but the statement in Reason R is accurate.

1. Assertion (A): A simple pendulum of fixed length has a constant time period at a given place.
Reason (R): The time period depends only on length and not on mass of bob.

2. Assertion (A): Sundials are not useful on overcast days.
Reason (R): Sundials require direct sunlight to cast a shadow.

3. Assertion (A): The Ghatika-yantra was announced by drums or conch shells when it sank.
Reason (R): It was used only for religious rituals and not for daily timekeeping.

4. Assertion (A): Atomic clocks are more accurate than pendulum clocks.
Reason (R): They use rapid vibrations of atoms instead of mechanical swings.

5. Assertion (A): A car moving in city traffic generally shows non-uniform motion.
Reason (R): It covers unequal distances in equal intervals of time due to traffic signals.

6. Assertion (A): Speed = Total distance / Total time gives average speed.
Reason (R): Objects rarely move at constant speed throughout a journey.

7. Assertion (A): Two pendulums of same length but different bob masses have same time period.
Reason (R): Mass does not affect the time period of a simple pendulum.

8. Assertion (A): The Samrat Yantra can measure time intervals as short as 2 seconds.
Reason (R): Its shadow moves very slowly, about 1 mm per second.

9. Assertion (A): A runner completing 400 m in 45 seconds is faster than one completing in 50 seconds.
Reason (R): Less time for same distance means greater speed.

10. Assertion (A): Water clocks with outflow are less accurate than sinking bowl types.
Reason (R): Flow rate in outflow clocks decreases as water level drops.

Science Class 7 CBQ of Measurement of Time and Motion

11. Assertion (A): All ancient sundials were completely useless for tracking time during night hours or heavy overcast days.
Reason (R): Sundials rely strictly on the changing position of a shadow cast by an object via the direct light of the Sun.

12. Assertion (A): The sinking bowl water clock (Ghatika-yantra) was progressively phased out and replaced by pendulum clocks in India from the late 19th century onward.
Reason (R): The Ghatika-yantra relied on a bowl with a fine hole at the bottom that filled up and sank in a fixed, repeatable interval of time.

13. Assertion (A): If you increase the mass of a simple pendulum’s bob from 50 grams to 500 grams, its time period will increase tenfold.
Reason (R): The time period of a simple pendulum depends entirely on the length of its suspending string and is independent of the mass of its bob.

14. Assertion (A): Quartz clocks and modern atomic clocks provide immensely higher precision than the original mechanical pendulum clocks.
Reason (R): Modern timekeeping instruments utilize tiny, incredibly rapid, and highly stable periodic vibrations from crystals or specific atoms.

15. Assertion (A): Writing the speed of an express delivery truck as “65 km/hrs” or “18 sec” is scientifically correct.
Reason (R): Symbols of scientific units are always written in lowercase singular forms and should not feature a trailing full stop unless completing a sentence.

16. Assertion (A): In everyday life, the speed we calculate for an automobile traveling between two towns is almost always its average speed.
Reason (R): Most moving bodies do not maintain a completely constant speed over long distances or time intervals due to practical real-world conditions.

17. Assertion (A): An odometer is fitted into motor vehicles to measure the live, real-time speed of the vehicle at any given split second.
Reason (R): A speedometer displays velocity metrics directly in kilometers per hour (km/h).

18. Assertion (A): An object moving along a straight track covering unequal distances in equal intervals of time is said to be in uniform linear motion.
Reason (R): Uniform linear motion occurs when an object travels equal distances over equal periods of time.

19. Assertion (A): For races covering the exact same distance (like a 100-meter dash), the runner who takes the shortest amount of time is declared the fastest.
Reason (R): Speed is calculated mathematically as the total distance covered divided by the total time taken to cover it.

20. Assertion (A): Scientists continue to develop timekeeping instruments that can measure tiny fractions of a second, down to milliseconds and microseconds.
Reason (R): Accurate tracking of fractional time intervals is critical for modern systems like sports timing, medical heart monitors, and computer signal processing.

Science Class 7 CBQ of Measurement of Time and Motion

Answer Key & Reference Guide

Section A:

Q. No.	Answer	Explanation
1	c) Second	The SI base unit for time is the second (symbol: s).
2	c) Hourglass	An hourglass tracks time through the controlled movement of sand from one bulb to another.
3	c) Christiaan Huygens	Huygens invented and built the first pendulum clock in 1656, greatly improving timekeeping accuracy.
4	c) Time period	The time period is the duration to complete one full oscillation.
5	b) Odometer	An odometer records the total distance traveled (in km or miles).
6	b) Length of the string	For a simple pendulum, T = 2π√(L/g), so the time period depends only on length (L) and gravity (g), not mass or color/material of the bob.
7	c) Sundial	The Samrat Yantra in Jaipur’s Jantar Mantar is a large sundial (equatorial dial).
8	a) 5 m/s	Speed = distance/time = 100 m / 20 s = 5 m/s.
9	c) Uniform linear motion	Constant speed on a straight track means both speed and direction are constant → uniform linear motion.
10	b) Ghatika-yantra	In ancient India, the sinking bowl water clock was known as Ghatika-yantra or Ghati.
11	C) Candle Clock – Consumption of fuel marked with time passages	Candle clocks mark time by the fuel (wax) consumed. Other pairings: A) Sundial uses shadow, not sand. B) Ghatika-yantra uses water, not shadow. D) An hourglass relies on sand rather than a floating bowl.
12	B) Jaipur	The Samrat Yantra is the iconic large sundial at Jantar Mantar, Jaipur.
13	C) The flow rate decreased as the water level dropped	Lower water height = lower pressure = slower outflow, making outflow-type water clocks non-linear and inaccurate.
14	B) Christiaan Huygens	Patented in 1656–1657. Galileo had designed one but did not build or patent it before his death.
15	A) Mean position	When hanging straight down (at rest), the bob is at the mean (equilibrium) position.
16	C) From mean position O to extreme A, then to extreme B, and back to O	One full oscillation returns the bob to the starting point with same direction of motion.
17	C) Second (s)	SI unit of time is the second; its official symbol is “s” (lowercase, not “sec”).
18	D) 10 h	Correct format for hour: no period after symbol, space between number and symbol. Using ’15 sec’ is incorrect—the proper format is ’15 s.’ Similarly, ‘4 hrs’ is wrong, and including a period after the symbol as in ’20 s.’ is also incorrect.
19	B) Speedometer	The speedometer provides a real-time reading of a vehicle’s speed, often expressed in km/h or mph.
20	B) Uniform linear motion	Unchanging constant speed along a straight path = uniform linear motion.

Science Class 7 CBQ of Measurement of Time and Motion

section b:

Q.No.	Answer	Explanation
1	b) 1.5 s	Time period = Total time ÷ Number of oscillations = 30 s ÷ 20 = 1.5 s.
2	a) Time period of longer pendulum is double	T ∝ √L. For lengths L and 4L, ratio T₁/T₂ = √(L/4L) = 1/2 → T₂ = 2T₁.
3	b) Flow rate decreases with lower pressure	Lower water height = lower pressure at the outflow hole → slower flow → inaccuracy.
4	a) 250 m	90 km/h = 90 × (1000/3600) = 25 m/s. Distance = 25 × 10 = 250 m.
5	c) Both have same speed	Runner 1: 100/12 = 8.33 m/s. Runner 2: 200/24 = 8.33 m/s. Same speed.
6	b) Flow rate remained more constant	Floating bowl (sinking type) maintained a more constant head of pressure, improving accuracy.
7	b) Time period increases, clock loses time	Longer length → larger time period → pendulum swings slower → clock loses time.
8	b) 10	Loss rate = 1 s per 1 million years. In a period of 10 million years, about 10 seconds are lost.
9	a) Both had same average speed	Average speed = total distance / total time. Average speed is unchanged if both the distance and the time are the same.
10	b) It depends on the Sun’s shadow	Sundial requires sunlight to cast a shadow; no shadow at night or under clouds.
11	b) 4 m/s	3.6 km = 3600 m, 15 min = 900 s. Speed = 3600/900 = 4 m/s.
12	c) 4 hours	Time = Distance / Speed = 360 km / 90 km/h = 4 hours.
13	c) Both pendulums will have the exact same time period	Time period of simple pendulum is independent of bob mass (T = 2π√(L/g)).
14	b) Your own resting pulse beat	Galileo reportedly used his pulse to time pendulum swings before mechanical clocks existed.
15	b) It natively measures local solar time based on its specific geographic longitude	Samrat Yantra shows local solar time of Jaipur; IST requires longitude correction (∼82.5° E).
16	c) 240 km	Average speed = total distance ÷ total time = 180 km ÷ 3 h = 60 km/h. In 4 hours: 60 × 4 = 240 km.
17	b) The train is faster than the horse	With a speed of 18 m/s for the horse and 72 km/h for the train—equivalent to 20 m/s—the train moves 2 m/s faster than the horse.
18	c) One-millionth of a second	Microsecond = 10⁻⁶ s = one-millionth of a second.
19	b) Friction, traffic, and environmental constraints cause real-world objects to constantly change speed	Uniform linear motion (constant speed + straight line) is idealized; real motion has speed fluctuations.
20	c) 20 m/s	First 500 m at 10 m/s → time = 500/10 = 50 s. Next 500 m at 5 m/s → time = 500/5 = 100 s. Total used = 150 s. Remaining time = 200 − 150 = 50 s. Remaining distance = 1000 m. Speed = 1000/50 = 20 m/s.

Science Class 7 CBQ of Measurement of Time and Motion

section c:

Q.No.	Answer	Explanation
1	A) 1.50 s	Average time for 10 oscillations = (15.0+15.2+14.8)/3 = 45.0/3 = 15.0 s. Time period = 15.0/10 = 1.50 s.
2	A) 1.41	T ∝ √L. Doubling length multiplies T by √2 ≈ 1.41.
3	A) 5 m/s	Each 10 s covers 50 m → speed = 50/10 = 5 m/s (constant).
4	C) Both have the same average speed	Athlete 1: 400/50 = 8 m/s. Athlete 2: 200/25 = 8 m/s. Same average speed.
5	B) 72 km/h	A to C: distance = 180 km, time = 2.5 h (10:00 to 12:30). Speed = 180/2.5 = 72 km/h.
6	A) 3.5 m/s	Total distance = 10+15+20+25 = 70 m. Total time = 20 s. Speed = 70/20 = 3.5 m/s.
7	A) 2.00 s	Average = (2.01+1.99+2.00+2.02+1.98)/5 = 10.00/5 = 2.00 s (most accurate).
8	C) ~8.3 m	Speeds: X=8.0 m/s, Y≈7.69 m/s, Z≈8.33 m/s. When Z finishes (12 s), Y runs 7.69×12=92.3 m → behind by 100−92.3=7.7 m (~8.3 m with rounding).
9	C) Time period is independent of mass	All time periods ~2.00 s despite mass varying 50–200 g.
10	C) ~240 s	Time increases faster than linearly (30,85,155). Differences: 55,70 → next ~85 → 155+85=240 s.
11	C) 40 km	At 10:20 position = 40 km, at 10:40 position = 80 km → distance = 40 km.
12	B) Train Y	Train X covers constant 20 km/interval (uniform). Train Y: 20,15,15,25,20,25 (non-uniform).
13	B) Train X, because it covers an identical, constant distance of 20 km during every single 10-minute time interval	Uniform linear motion = equal distances in equal time intervals.
14	C) 120 km/h	Total distance = 120 km (10:00 to 11:00). Time = 1 hour → speed = 120 km/h.
15	B) 10:10 AM – 10:30 AM	This is two intervals (10:10–10:20: 15 km, 10:20–10:30: 15 km). Slowest single interval = 15 km (also 10:50–11:00 is 20 km). But question says “10-minute data-tracking interval” — slowest is 15 km, which occurs at 10:10–10:20 and 10:20–10:30. The listed option B covers both but they likely mean 10:10–10:20.
16	B) 3.15 s	T ∝ √L. For L=250, √250=15.81. From L=160 (√=12.65, T=2.52): T = 2.52 × (15.81/12.65) ≈ 2.52 × 1.25 = 3.15 s.
17	A) 0.8 m/s	From 0–10 s: distance 8 m → speed = 8/10 = 0.8 m/s (constant uniform motion).
18	B) 16 meters	At 20 s: distance = speed × time = 0.8 × 20 = 16 m.
19	C) 56 meters	At 70 seconds, the distance covered is 0.8 multiplied by 70, which equals 56 meters.
20	B) Non-Uniform	Distances per 10 s: 6,4,6,5,8,6,7,3,10,5 → not constant → non-uniform.
21	C) 60 meters	The table shows that at the 100-second mark, the distance traveled is 60 m.
22	A) 0.6 m/s	Average speed = total distance / total time = 60 m / 100 s = 0.6 m/s.
23	C) 70 s to 80 s	The smallest change in distance occurs from 70 to 80 seconds, where it rises by just 3 m (from 42 m to 45 m).

Science Class 7 CBQ of Measurement of Time and Motion

section d:

Q.No.	Answer Option	Explanation
1	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A is true (fixed length → constant period at given place). R correctly explains why: period depends on length, not mass.
2	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A: Sundials fail on overcast days. R correctly gives reason (need direct sunlight for shadow).
3	c) Assertion A holds true; however, the reason given in R is factually incorrect.	A is true (drums/conch announced sinking). R is false (Ghatika-yantra was used for daily timekeeping, not only rituals).
4	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (atomic clocks more accurate). R explains why (atomic vibrations are faster/more stable than mechanical swings).
5	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (city traffic → non-uniform motion). R correctly explains (unequal distances due to signals).
6	b) A is true and R is also true, but R does not logically justify or clarify A.	A true (definition of avg speed). R true (objects rarely have constant speed) but does not explain the formula in A.
7	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (same length → same period regardless of mass). R correctly gives the reason (mass doesn’t affect period).
8	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (Samrat Yantra can measure ~2 s). R correctly explains (shadow moves ~1 mm/s → 2 mm resolution → ~2 s).
9	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (45 s runner is faster). R correctly explains (less time for same distance → greater speed).
10	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (outflow less accurate than sinking bowl). R correctly explains (outflow rate drops with water level).
11	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (sundials useless at night/overcast). R correctly explains (need direct sunlight for shadow).
12	b) A is true and R is also true, but R does not logically justify or clarify A.	A true (Ghatika-yantra replaced by pendulum clocks in late 19th century India). R true (describes how it works) but does not explain why it was phased out (better accuracy of pendulum clocks).
13	d) Assertion A is not valid, but the statement in Reason R is accurate.	A false (increasing mass does not increase period tenfold; period independent of mass). R true (period depends on length, not mass).
14	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (quartz/atomic clocks more precise than mechanical pendulum clocks). R correctly explains (faster, stable vibrations from crystals/atoms).
15	d) Assertion A is not valid, but the statement in Reason R is accurate.	A false (65 km/hrs and 18 sec are incorrect; correct: 65 km/h, 18 s). R true (SI symbols are lowercase singular, no trailing period).
16	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (calculated speed between towns is average speed). R correctly explains (real-world motion not constant).
17	d) Assertion A is not valid, but the statement in Reason R is accurate.	A false (odometer measures distance, not speed). R true (speedometer measures km/h).
18	d) Assertion A is not valid, but the statement in Reason R is accurate.	A false (unequal distances in equal times = non-uniform motion). R true (correct definition of uniform linear motion).
19	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (shortest time → fastest). R correctly explains (speed = distance/time → less time → higher speed).
20	a) Both A and R are factually correct, and R provides the precise logical explanation for A.	A true (scientists measure ms/μs). R correctly explains (critical for sports, medical, computer systems).

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