CBSE Class 7 Science Chapter 01 The Ever Evolving World Of Science MCQs Set 01

Answer: (D) The rotation of stars around the Earth

Explanation:
Humans observed the rising and setting of the Sun, the phases of the Moon, and the changing seasons as examples of natural events repeating after definite intervals. The rotation of stars around the Earth is not mentioned as one of these natural cycles used for timekeeping.

Answer: (C) Water flowing out of or into a vessel to mark time passage

Explanation:
Water clocks measured time using the flow of water either out from a marked vessel or into a floating bowl. This flow mechanism was the key feature distinguishing water clocks from other ancient timekeeping devices.

Answer: (A) The flow rate decreased as water levels dropped; the Ghatika-yantra used a floating bowl that sank at a constant rate instead

Explanation:
• Outflow-type water clocks became less accurate because their flow rate decreased as water levels in the vessel dropped
• The Ghatika-yantra solved this by using a floating bowl that filled and sank at a constant rate, independent of water level
• This made it a more reliable timekeeping design than the earlier outflow clocks

Answer: (B) Galileo Galilei

Explanation:
Galileo Galilei noticed a suspended lamp swinging in a church and, using his pulse to measure time, found that each swing took the same duration. This observation inspired his later investigations into pendulums.

Answer: (B) Movement from mean position to one extreme, then to the other extreme, and back to mean position

Explanation:
One complete oscillation involves the bob starting from the mean position, moving to extreme position A, changing direction to extreme position B, and returning to the mean position O. Alternatively, it can be measured from one extreme to the other extreme and back.

Answer: (B) To verify that the time period remains almost constant across multiple trials

Explanation:
Repeating the measurement multiple times allowed students to observe and confirm that the time period of a pendulum of given length is constant at a place. This repeated observation supports the fundamental property of simple pendulums used in timekeeping.

Answer: (B) Their precision—atomic clocks lose only one second in millions of years compared to gaining or losing 10 seconds per day

Explanation:
Huygens' early pendulum clocks could gain or lose 10 seconds each day, while modern atomic clocks are so precise they lose only one second in millions of years. This represents a dramatic improvement in accuracy.

Answer: (B) The time period depends on the length but not on the bob's mass

Explanation:
The "Think Like a Scientist" section and the Ghatika-yantra discussion show that different string lengths produce different time periods. The text explicitly states that the time period depends on length but not on the bob's mass, and all pendulums of the same length have the same time period at a given location.

Answer: (B) Which object covers more distance within the same time interval

Explanation:
Someone who has covered more distance within the same time is running faster. This comparison of distances in a given time interval is the fundamental way to determine relative speeds.

Answer: (B) Metre per second, derived from dividing distance (in metres) by time (in seconds)

Explanation:
Since speed is calculated as distance divided by time, and the SI unit of distance is metre while the SI unit of time is second, the SI unit of speed is metre per second (m/s).

Answer: (A) It reveals the pattern in how train type relates to speed, showing which type covers the most distance in the least time

Explanation:
By calculating speeds for multiple train types on the same route, students observe that Superfast trains cover greater distances in the same time than Passenger or Express trains. This comparison illustrates the practical concept that speed determines which vehicle is faster, and helps students identify the relationship between train type and speed.

Answer: (B) In uniform motion, equal distances are covered in equal time intervals; in non-uniform motion, unequal distances are covered in equal time intervals

Explanation:
An object in uniform linear motion covers equal distances in equal intervals of time, while it covers unequal distances in equal intervals of time when in non-uniform motion. Table 8.3 demonstrates this distinction using trains X and Y as examples.

Answer: (B) Train X, because it covered 20 km in every 10-minute interval

Explanation:
• Train X covered exactly 20 km in each 10-minute interval from start to finish
• Train Y covered varying distances: 20 km, then 15 km, then 15 km, then 25 km, then 20 km, then 25 km
• Equal distances in equal time intervals is the definition of uniform motion, which only Train X satisfied

Answer: (C) Because real-world objects rarely move at constant speed, but average speed provides a useful measure of overall motion efficiency

Explanation:
In everyday life, objects seldom move with constant speed over long distances or long time intervals. Using average speed—calculated as total distance divided by total time—provides a practical way to describe and compare the overall motion of objects, even when their speed fluctuates throughout the journey.

Answer: (A) A pendulum's swing always takes the same time regardless of how wide it swings

Explanation:
Galileo observed a swinging lamp in a church and used his pulse to measure time. He found that each swing took the same duration, regardless of the amplitude. This property inspired Huygens to create a mechanical clock using pendulums, since their consistent timing could reliably mark equal intervals of time.

Answer: (B) Tiny differences in arrival time—down to fractions of a second—can determine the actual winner

Explanation:
Modern timekeeping can measure hundredths or even thousandths of a second, allowing officials to determine winners in races where sprinters appear to finish simultaneously to the naked eye. Without such precision, determining the actual winner would be impossible.

Answer: (B) Markings on the container correspond to equal time intervals

Explanation:
By marking water levels at one-minute intervals while observing an actual watch, students calibrate their water clock so that each mark represents an equal passage of time. When water reaches each mark, one more minute has elapsed—making the device a functional timekeeper.

Answer: (A) 10 m/s

Explanation:
Speed = 72 km ÷ 2 h = 36 km/h. Converting to m/s: 36 km/h × (1000 m/km) ÷ (3600 s/h) = 36 × 1000 ÷ 3600 = 10 m/s.

Answer: (B) Non-uniform linear motion with changing speed

Explanation:
Since the runner's speed changes throughout the race—being faster on some stretches and slower on others—this is non-uniform linear motion, defined as occurring when an object's speed keeps changing while moving along a straight line.

Answer: (B) Its 1 millimetre-per-second shadow movement allows measurement of time intervals as short as 2 seconds

Explanation:
The Samrat Yantra's imposing height creates a shadow that moves at precisely 1 millimetre per second, allowing it to measure remarkably short time intervals of 2 seconds or less. This precision made it an exceptional ancient timekeeping instrument despite relying on solar position.

Answer: (B) Vehicles in real situations constantly adjust their speed due to various factors like traffic, slopes, and stops

Explanation:
Real-world motion involves countless variables—acceleration, deceleration, stops, and obstacles—making truly constant speed rare. This is why average speed is emphasised for practical calculations rather than assuming uniform motion throughout a journey.

Answer: (B) Arthasastra

Explanation:
The Arthasastra by Kautilya is one of the early texts describing the outflow-type water clock, along with the Sardulakarnavadana and some other texts from the early CE centuries.