Class 7 Science Curiosity Chapter 8 MCQ – Measurement of Time and Motion

A sundial uses the changing position of a shadow cast by sunlight. People can relate the shadow’s position to the time of day. The chapter presents this as an early method of timekeeping based on observations of nature.

An hourglass measures an interval by allowing sand to flow from one bulb into the other. The chapter includes it among devices used before modern clocks, alongside sundials, water clocks, and marked candles that measured the passage of time.

One ghatika was a time interval of 24 minutes. The sinking-bowl water clock was made to fill and sink in this time. The chapter explains that a full day of 24 hours was divided into 60 such intervals.

Christiaan Huygens invented the pendulum clock in 1656 and patented it in 1657. The chapter explains that Galileo’s investigations of pendulums helped inspire this invention, showing how observations can later contribute to the development of a useful measuring device.

The metallic ball suspended by the thread is called the bob. A simple pendulum has this bob hanging from a rigid support. When moved slightly to one side and released, it swings back and forth in oscillatory motion.

The time period is the time needed for one complete oscillation. In the activity, students measure the time for several oscillations and divide by their number, which gives the time for a single complete back-and-forth movement.

One oscillation brings the pendulum back to its starting position after completing a full cycle. Starting at an extreme, it travels to the opposite extreme and returns. Reaching only the mean position or opposite extreme is not a complete cycle.

The chapter states that a pendulum’s time period depends on its length, but not on the bob’s mass. Keeping the location the same allows students to compare pendulums and investigate the effect of changing their lengths in the activity.

The SI unit of time is the second, written with the symbol s. The chapter also stresses correct unit notation: symbols are written in their standard form, without changing them into plurals or using informal abbreviations such as sec.

Average speed tells us the distance covered per unit time over the whole journey. Dividing the total distance by the total time gives this value, even if the object travelled faster during some parts and slower during other parts.

Speed is distance divided by time. Using the SI unit metre for distance and second for time gives metre per second, written m/s. The chapter also uses km/h when distance is measured in kilometres and time in hours.

Uniform linear motion combines a straight path with constant speed. The object therefore covers equal distances in equal time intervals. The chapter contrasts this with non-uniform linear motion, where the speed changes while the path remains straight.

In non-uniform linear motion, an object moves along a straight line but its speed changes. A train speeding up after departure or slowing down before a station is used to explain this difference from motion at constant speed.

A speedometer measures and displays the vehicle’s speed, commonly in kilometres per hour. The chapter distinguishes it from an odometer, which measures distance travelled. Knowing this difference helps us identify the information shown by the two instruments.

An odometer records the distance travelled by a vehicle, usually in kilometres in the chapter’s example. It does not show how fast the vehicle is moving at that moment; that different quantity is displayed by the speedometer.

Dividing 150 metres by 10 seconds gives 15 metres per second. In one hour, that rate covers 15 × 3600 = 54000 metres. Since 1000 metres equal one kilometre, the speed is 54 kilometres per hour. The conversion changes the unit used, not the actual speed.

First convert 360 kilometres to 360000 metres so that the distance unit matches the speed. Time equals distance divided by speed: 360000 ÷ 25 = 14400 seconds. Dividing by 3600 seconds per hour gives a journey time of four hours.

Average speed is total distance divided by total time. Here, 180 kilometres divided by three hours gives 60 kilometres per hour. This describes the journey as a whole and does not require the train’s speed to be constant throughout.

Convert the train’s speed to metres per second: 72 kilometres per hour equals 72000 ÷ 3600 = 20 metres per second. The horse travels at 18 metres per second, so the train is faster by two metres per second.

The car covers unequal distances in equal one-hour intervals, so its motion is non-uniform. Its total distance is 60 + 70 + 50 = 180 kilometres. Dividing by the total time of three hours gives an average speed of 60 kilometres per hour.

The time period is the time for one oscillation. Divide the measured time by the number of oscillations: 40 ÷ 20 = 2 seconds. This follows the chapter’s method of measuring several oscillations and calculating the time for one.

The chapter states that the time period depends on length and not on the bob’s mass at a given location. Keeping the lengths and location the same therefore gives approximately equal periods despite the different masses of the bobs.

Convert the distance to 1800 metres and the time to 300 seconds. Average speed is then 1800 ÷ 300 = 6 metres per second. Converting both measurements before dividing ensures that the result uses the requested unit correctly.

Distance is calculated by multiplying speed by time. The bus travels 40 kilometres each hour for 2.5 hours, so the distance is 40 × 2.5 = 100 kilometres. The units match because the speed and time both use hours.

Time equals distance divided by speed. Dividing 120 kilometres by 40 kilometres per hour gives three hours. This means that covering 40 kilometres in each hour takes three such intervals to complete the full 120-kilometre journey.

Runner P’s average speed is 200 ÷ 40 = 5 metres per second. Runner Q’s is 300 ÷ 50 = 6 metres per second. Because their distances differ, we compare distance per unit time rather than the times alone. A shorter running time alone does not establish greater speed.

The total distance is 90 + 60 = 150 kilometres, and the total time is 2 + 1 = 3 hours. Dividing total distance by total time gives 50 kilometres per hour. We cannot simply average the two stage speeds because the two parts take different amounts of time.

The object covers equal distances in equal time intervals on a straight path, so its motion is uniform and linear. Its speed is 12 ÷ 4 = 3 metres per second, using the relationship between distance and time.

The time intervals are equal, but the distances covered are different. This means the object’s speed changes during the observation. Because the path is straight, the chapter’s term for this situation is non-uniform linear motion.

The first 400 metres take 400 ÷ 4 = 100 seconds. This leaves 800 metres and 100 seconds for the rest of the journey. Dividing the remaining distance by the remaining time gives the required average speed of 8 metres per second.