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Class 7 Science Chapter 8 Measurement of Time and Motion Extra Questions
Class 7 Science Chapter 8 Extra Questions on Measurement of Time and Motion
Measurement of Time and Motion Class 7 Very Short Question Answer
Question 1.
What is a motion?
Answer:
Motion is defined as there is a change in the position of an object with respect to its surroundings with time.
Question 2.
Define speed.
Answer:
The distance travelled by an object in unit time is known as speed of the object.
Speed = \(\frac{\text { Distance covered }}{\text { Time taken }}\)
Question 3.
If Vijay covers a certain distance in one hour and Ram covers the same distance in two hours, who travels at a higher speed?
Answer:
Vijay travels with a higher speed, as he covers the same distance in lesser time than Ram.
Question 4.
A simple pendulum is oscillating between two points A and B as shown in figure. Is the motion of the bob uniform or non-uniform?
Answer:
The motion of the bob is non-uniform because the speed of the bob keeps changing as it does not cover equal distance in equal intervals of time.
(a) A simple pendulum
(b) Different positions of the bob of an oscillating simple pendulum
Question 5.
What is SI unit of speed?
Answer:
The SI unit of speed is meter per second (m/s).
Question 6.
What do you mean by uniform motion?
Answer:
An object moving along a straight line with a constant speed is said to be in uniform linear motion.
Question 7.
What do you mean by non – uniform motion?
Answer:
If the speed of an object moving along a straight line keeps changing, it is said to be in non-uniform linear motion.
Question 8.
Define time period.
Answer:
The time taken by the pendulum to complete one oscillation is called its time period
Question 9.
What is an oscillatory motion?
Answer:
The to and fro motion of an object about a fixed point is called oscillatory motion.
Question 10.
Give any two examples of periodic motion.
Answer:
Examples of periodic motion are:
- Rotation of earth on its axis.
- Revolution of the Moon around the earth.
Question 11.
What is speedometer?
Answer:
Speedometer is a device on a vehicle’s dashboard, which indicates the speed of the vehicle.
Question 12.
What is bob?
Answer:
The metallic ball is called bob of the pendulum.
Question 13.
What is odometer?
Answer:
Odometer is an instrument for measuring the distance travelled by the vehicle. It records the distance travelled by the vehicle in kilometre.
Question 14.
Where will you find speedometers and odometers?
Answer:
Speedometers and odometers will be seen on the dashboards of buses, cars, scooters and motor bikes.
Question 15.
What devices do we use to measure intervals of time which are much shorter than a day?
Answer:
The most common time measuring devices used are docks or watches.
Measurement of Time and Motion Class 7 Short Question Answer
Question 1.
What do you understand by periodic motion? Give two examples.
Answer:
The motion which repeats itself after regular intervals of time, is called periodic motion.
Examples:
- The motion of the swing, to and fro motion of a simple pendulum.
- The rotation of the earth on its axis, and the revolution of the earth around the sun.
Question 2.
What do you mean by the statement; “car is moving with the speed of 50 km per hour”?
Answer:
Car is moving with the speed of 50 km per hour it means it will cover a distance of 50 km in one hour.
Question 3.
A spaceship travels 36000 km in one hour. Express its speed in km/s.
Answer:
Given, Distance travelled by spaceship = 36000 km
Time taken = 1 hour
We know, 1 hour = 60 min
= 60 × 60 = 3600 seconds
Speed = \(\frac{\text { Distance travelled }}{\text { Time taken }}\)
= \(\frac{36000}{3600}\)
= 10 km/s
Question 4.
A boy runs 20 km in 2 hours. How long will he take to run 40 km at double the previous speed?
Answer:
A boy runs 20 km in 2 hours.
Speed = \(\frac{\text { Distance travelled }}{\text { Time taken }}\)
= \(\frac{20}{2}\) =10 km/h
He will take time to run 40 km at double the previous speed is (40/20) = 2 hours.
Question 5.
Why do we need to measure time?
Answer:
We need to measure the time for the following and many more reasons:
- Doctors need to measure the pulse rate or heart rate of a patient.
- Farmers need to measure the time between sowing and harvesting of crops.
- A sportsman needs to measure the time he might take to complete an event.
- A traveller needs to measure the time of his journey.
- Students need to measure the time to complete an examination or a test in a given time slot.
Question 6.
What are the differences between slow and fast motion?
Answer:
The differences between slow and fast motion
| Slow motion | Fast motion |
| 1. When an object takes a long time to cover a certain distance it is known to have a slow motion. | When an object takes shorter time to cover certain distance it is known to have a fast motion. |
| 2. Example: Motion of a tortoise or a snail. | Example: Racing car or a leopard. |
Question 7.
What are the factors on which the time period of a pendulum depends?
Answer:
The time period of a simple pendulum does not depend on the mass of the bob and nature of the material of the bob. It depends upon the length of the pendulum and acceleration due to gravity.
Question 8.
The average age of children of class VII is 12 years and 3 months. Express this age in second.
Answer:
Given, the average age of children is 12 years and 3 months
1 year = 365 days = 365 × 24 h [1 day = 24 h]
= 365 × 24 × 3600 s [1 h = 3600 s]
12 years = 31536000 s × 12 = 378432000 s
3 months = 30 × 3 days = 30 × 3 × 24h
= 30 × 3 × 24 × 3600s = 7776000s
So, total age in second = 378432000 + 7776000 = 386208000 s.
Question 9.
Find the speed of a car that travels in 500 km in 5 hours.
Answer:
Given, distance covered = 500 km and Time taken = 5 hours
Speed = \(\frac{\text { Distance travelled }}{\text { Time taken }}\)
= \(\frac{500}{5}\)
= 100 km/h
Hence, speed = 100 km/h
Question 10.
Convert 36 km/h into m/s.
Answer:
To convert 36 km/h into m/s; Multiply by \(\frac{5}{18}\)
1 km = 1000 m and 1 hour = 3600s
1 km/1 hour = \(\frac{3600}{1000}\) = \(\frac{5}{18}\) km/h
36 km/h = 36 × \(\frac{5}{18}\) m/s = 10 m/s.
Measurement of Time and Motion Class 7 Long Question Answer
Question 1.
Write the differences between uniform motion and non-uniform motion.
Answer:
The difference between uniform motion and non-uniform motion are as follows:
| Uniform motion | Non-uniform motion |
| 1. An object moving along a straight line with a constant speed is said to be in uniform motion. | An object moving along a straight line with variable speed is said to be in non-uniform motion. |
| 2. It covers equal distances in an equal interval is of time. | It covers unequal distances in equal intervals of time. |
| 3. Average speed is equal to the actual speed of the object. | Average speed is not equal to actual speed of the object. |
Question 2.
The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.
Answer:
Initial reading of car odometer = 57321.0 km
Final reading of car odometer = 57336.0 km
Time at the time of initial reading = 08:30 AM
Time at the time of final reading = 08:50 AM
Distance travelled by the car = 57336.0 km – 57321.0 km =15 km
Time taken by the car to cover distance = 08:50 AM – 08:30 AM = 20 min
Speed of the car in km/min = 15 km/20 min = 0.75 km/min
Speed of the car in km/h = 15 km/20 × 60 h = 45 km/h
Question 3.
Vijay covers a distance of 2.4 km from his house to reach her college on a scooter. If the scooter has a speed of 6 m/sec, calculate the time taken by him to reach the college.
Answer:
Total distance travelled =2.4 km
= 2.4 × 1000 m
= 2400 m.
Speed = 6 m/sec
Now, time = (Distance/speed)
= 2400/6 = 400 sec.
Measurement of Time and Motion Class 7 Case-Based Questions
I. Pooja and Manvi sat on swings in the playground. Anita noticed that the swing moved back and forth in equal intervals. Their teacher explained that a swing behaves like a simple pendulum. Each complete back-and-forth motion is called an oscillation. They used this swing motion to measure time and compare it with their wristwatches.
Answer the following questions:
Question 1.
What is one complete to and fro motion of a pendulum called?
(a) Rotation
(b) Revolution
(c) Oscillation
(d) Cycle
Answer:
(c) A full back-and-forth move¬ment of a pendulum is known as one oscillation.
Question 2.
Which instrument works on the principle of oscillations?
(a) Thermometer
(b) Water clock
(c) Pendulum clock
(d) Compass
Answer:
(c) Pendulum clocks keep time using the regular oscillations of a pendulum.
Question 3.
The time taken for one oscillation is called:
(a) Frequency
(b) Time period
(c) Speed
(d) Pulse rate
Answer:
(b) The time taken to complete one oscillation is called the time period.
Question 4.
If a pendulum completes 20 oscillations in 10 seconds, what is the time period of one oscillation?
(a) 0.2 seconds
(b) 2 seconds
(c) 0.5 seconds
(d) 10 seconds
Answer:
(c) Time period
= \(\frac{\text { Total time }}{\text { Number of oscillations }}\)
= 10 ÷ 20
= 0.5 seconds.
Measurement of Time and Motion Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
Define uniform linear motion.
Question 2.
Write the formula of speed.
Question 3.
What is non-uniform motion?
Question 4.
What do you mean by simple pendulum?
Question 5.
What is a quartz clock?
Short Answer Type Questions
Question 1.
Explain speedometer and odo meter.
Question 2.
What do you know about measurement of time in ancient and modern periods?
Long Answer Type Questions
Question 1.
From the definition of speed, draw the relationship between distance, time and speed.
Question 2.
How do you derive the conversion formula for units of speed from „ m/s to km/h? Which speed is higher of the two in
(i) 10 m/s and 36 km/h?
(ii) 15 m/s and 72 km/h?
Case/ Source Based Questions
I. The pendulum at rest is in its mean position. When the bob of the pendulum is moved slightly to one side and released, it starts oscillatory motion.
Its motion is periodic in nature because it repeats its path after a fixed interval of time.
Question 1.
What is the type of motion a simple pendulum shows?
Question 2.
Is oscillatory motion also a periodic motion? Explain.
Question 3.
What is the time period of a simple pendulum?
Question 4.
What is the oscillation of a simple pendulum?