## Samacheer Kalvi 9th Term III Science Book Back Question and Answers – Unit 3:

Samacheer Kalvi 9th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 9 New Syllabus 2021 to 2022 Book Back Question & Answer solutions available for both English and Tamil Medium. Class 9 Science Book Term 3 Unit 3 – Universe Answers/Solutions are provided on this page. 9th Std Science Book is of Term 1st, 2nd, 3rd, and consists of 9 Units in each Term. All 9 Units of Term 1st, 2nd, 3rd Science Book Back One, and Two Mark Solutions are given below.

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### Samacheer Kalvi 9th Science Book Back Term 3 Unit 3 Solutions Guide PDF:

Science Subject 1 Mark and 2 Mark Solutions Guide PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes.

### I. Choose the correct answer:

1. Which of the following statement is correct?
A) There are eight planets in our solar system.
B) Except Mars all other planets revolve around the Sun in elliptical orbits.
a) A only                b) B only
c) Both A and B      d) None

2. Who proposed the heliocentric model of the universe?
a) Tycho Brahe   b) Nicolaus Copernicus
c) Ptolemy          d) Archimedes

3. Which of the following is not a part of outer solar system?
a) Mercury   b) Saturn
c) Uranus        d) Neptune

4. Ceres is a
a) Meteor    b) Star
c) Planet     d) Asteroid

5. The period of revolution of planet A around the Sun is 8 times that of planet B. How many times is the distance of planet A as great as that of planet B?
a) 4    b) 5
c) 2     d) 3

6. The Big Bang occurred years ago.
a) 13.7 billion   b) 15 million
c) 15 billion          d) 20 million

### II. Fill in the blanks:

1. The speed of the Sun in km/s is 250km/s.
2. The rotational period of the Sun near its pole is 36 days.
3. India’s first satellite is Aryabhatta.
4. The third law of Kepler is also known as the law of Harmonies.
5. Triton is the only moon in the solar system that moves in the opposite direction to the direction in which its planet spins.
6. The number of planets in our solar system is eight.

### III. True or False:

1. The distance between Saturn and Uranus is about 10 times as that between Earth and Mars. – True
2. ISS is a proof for international cooperation. – True
3. Halley’s comet appears after nearly 67 hours. – False
4. Satellites nearer to the Earth should have lesser orbital velocity. – False
5. Mars is called the red planet. – True

### IV. Match the following:

1. Jupiter       a) 17.2 hours
2. Mercury    b) 10.7 hours
3. Venus        c) 87.97 days
4. Saturn       d) 9 hours 55 min
5. Mars           e) 243 days
f) 87.97 days
g) 24 hours 37 min
Ans: 1- d; 2- c; 3-e; 4- b; 5- g

### V. Short Questions & Answers:

1. What is the solar system?
The Sun and the celestial bodies which revolve around it form the solar system.

2. What is a cosmic year?
The Sun travelling at a speed of 250 km per second (9 lakh km/h) takes about 225 million years to complete one revolution around the Milky Way. This period is called a cosmic year.

3. Define orbital velocity.
The horizontal velocity that has to be imparted to a satellite at the determined height so that it makes a circular orbit around the planet is called orbital velocity.

4. Define time period of a satellite.
Time taken by the satellite to complete one revolution round the Earth is called time period.
Time period, T = Distance covered
Orbital velocity

5. What is a satellite? What are the two types of satellites?
A body moving in an orbit around a planet is called satellite. The two types of satellites they are:
1) Natural satellites

6. Write a note on the inner planets.
The four planets grouped together in the inner solar system are Mercury, Venus, Earth and Mars. They are called inner planets. They have a surface of solid rock crust and so are called terrestrial or rocky planets. Their insides, surfaces and atmospheres are formed in a similar way and form similar pattern. Our planet, Earth can be taken as a model of the other three planets.

7. Write about comets in brief.
Comets are lumps of dust and ice that revolve around the Sun in highly elliptical orbits. Their period of revolution is very long. When approaching the Sun, a comet vaporizes and forms a head and tail. Some of the biggest comets ever seen had tails 160 million (16 crores) km long. This is more than the distance between the Earth and the Sun. Many comets are known to appear periodically. One such comet is Halley’s Comet, which appears after nearly every 76 years. It was last seen in 1986, it will next be seen in 2062.

8. First Law – The law of Ellipses:
The path of the planets about the Sun is elliptical in shape, with the center of the Sun being located at one of the foci.
Second Law – The Law of Equal Areas:
An imaginary line drawn from the center of the Sun to the center of the planet will sweep out equal areas in equal intervals of time.
Third Law – The Law of Harmonies:
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their semi major axis from the Sun.

9. Write short notes on Gaganyaan.
The Indian Space Research Organization (ISRO) had proposed its Indian Human Spaceflight Programme to be done by 2021/2022 according to ISRO Chairman, K.Sivan. The first crew is to consist of three astronauts to be taken to space with a spacecraft called Gaganyaan on a GSLV-III rocket.V.R.Lalithambika, a specialist in advanced launcher technologies, will help the project as Director of the Human Space Flight Project.

10. What factors have made life on Earth possible?
The Earth where we live is the only planet in the solar system which supports life. Due to its right distance from the Sun it has the right temperature, the presence of water and suitable atmosphere, and a blanket of ozone. All these have made the continuation of life possible on Earth.