# 9th Standard Science Guide Universe Book Back Answers in English

## Lesson 9 Universe

9th Science Guide: In this post, we will explore the book back answers for Lesson 9 on the Universe. The universe is a vast and fascinating subject, and this lesson covers various aspects such as the heliocentric model, the outer solar system, celestial bodies, the planetary revolution, the Big Bang, and more.

This 9th Science Universe Book Back Answers post aims to test and enhance your knowledge about the universe by providing the correct answers to multiple-choice questions, fill-in-the-blanks, true or false, and matching exercises. Additionally, it includes brief explanations for the answers, detailed descriptions of concepts, and numerical problem-solving to further deepen your understanding.

### I. Choose the correct answer

1. Who proposed the heliocentric model of the universe?

1. Tycho Brahe
2. Nicolaus Copernicus
3. Ptolemy
4. Archimedes

Ans: Nicolaus Copernicus

2. Which of the following is not a part of the outer solar system?

1. Mercury
2. Saturn
3. Uranus
4. Neptune

Ans: Mercury

3. Ceres is a _______

1. Meteor
2. Star
3. Planet
4. Astroid

Ans: Astroid

4. 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?

1. 4
2. 5
3. 2
4. 3

Ans: 2

5. The Big Bang occurred ________ years ago.

1. 13.7 billion
2. 15 million
3. 15 billion
4. 20 million

Ans: 13.7 billion

6. Which of the following statements is correct?

A. There are eight planets in our Solar System.
B. Except Mars, all other planets revolve around the Sun in elliptical orbits

1. A only
2. B only
3. Both A and B
4. None

Ans: A only

### II. Fill in the Blanks

1. The speed of Sun in km/s is _______.

Ans: 250 km/s

2. The rotational period of the Sun near its poles is ________.

Ans: 36 days

3. India’s first satellite is _______

Ans: Aryabhata

4. The third law of Kepler is also known as the Law of ________

Ans: Harmonies

5. The number of planets in our Solar System is _______

Ans: 8

6. _______ is the only moon in the solar system that moves in the opposite direction to the direction in which its planet spins.

Ans: Triton

### III. True or False

1. ISS is proof of international cooperation.

Ans: True

2. Halley’s comet appears after nearly 67 hours.

Ans: False

Correct Ans: Halley’s comet appears after nearly 76 years.

3. Satellites nearer to the Earth should have lesser orbital velocity.

Ans: False

Correct Ans: Satellites nearer to the Earth should have higher orbital velocity

4. Mars is called the red planet.

Ans: True

1. The distance between Saturn and Uranus is about 10 times as that between Earth and Mars.

Ans: False

Correct Ans: The distance between Saturn and Uranus is about 20 times as that between Earth and Mars.

### III. 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

1. What is solar system?

The sun and celestial bodies which revolve around it forms the solar system.

2. Define orbital velocity.

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

3. Define time period of a satellite.

The time taken by the satellite to complete one revolution around the Earth is called the time period

4. What is a satellite? What are the two types of satellites?

A body moving around a planet is called satellite.

Types:

• Natural satellites
• Artificial satellites

5. Write a note on the inner planets.

The first four planets which are very close to the solar system are called inner planets. They are Mercury, venus, earth and Mars.

1. Comets are lumps of dust and ice that revolve around the sun in highly elliptical orbits.
2. Their period of revolution is long
3. When approaching the sun a comet vapourizes and forms a head and tail
4. Example: Halley’s comet

7. State Kepler’s laws.

First Law – The law of Ellipses

The path of the planets about the sun is elliptical in shape, with the centre of the sun being located at one of the foci .

Second law – ( The law of equal areas)

The imaginary line drawn from the centre of the sun and the centre of the planet will seeeps out equal areas in equal intervals of time.

Third law – ( The law of harmonics)

The ratio of the squares of the period of any two planets is equal to the ratio of the cube of their semi major axis from the sun.

8. What factors have made life on Earth possible?

The factors which made life possible on Earth are:

1. Due to its right distance from the Sun, it has the right temperature.
2. The presence of water
3. suitable atmosphere.
4. A blanket of ozone.

9. Write short notes on Gaganyaan.

Gaganyaan is an Indian grewed orbital space craft intended to be the basis of the Indian human spaceflight programme. The space craft is being designed to carry three people with docking capability. The crewd vehicle is planned to be launched on ISRO’s GSLV rocket in 2022.

10. What is a cosmic year?

The time taken by the sun to complete one revolution with a speed of 250km/second. The value of one cosmic year is 225 million years.

1. Give an account of all the planets in the solar system.

• Our solar system consists of eight planets such as mercury, venus, earth, mars, jupiter, saturn, uranus and neptune.
• The first four planets mercury, Venus, earth and Mars are called inner planets since they are very close to the sun. The inner planets are called rocky or terristial planets.
• The planets jupiter,saturn,uranus and neptune are called outer planets since they are farther to the sun. the outer planets consists of hydrogen , helium and other gases in huge amounts.
• The outer planets have a dense atmosphere so they are called as gas giants or gaseous planets.
• The outer planets have rings where as the inner planets have no rings.
• Out of all the planets the only planet earth has living factors. Due to the right distance from the sun it has a right temperature, Presence of water, Suitable atmosphere A blanket of ozone supports for our life.
• Among the planets in the solar system all the planets have moon except mercury and venus.

2. Discuss the benefits of ISS.

Benifits of ISS:

• The eye tracking device built in it has proved ideal to be used in many laser surgeries
• The eye tracking technology is also heling disabled people with limited movement and speech
• Robotic arms developed for research in the ISS are providing significant help to the surgeons in removing inoperable tumours
• ISS also very helpful in the development of improved vaccines, breast cancer detectionand treatment, ultrasound machines for remote regions etc

3. Write a note on orbital velocity.

• The horizontal velocity that has to be imparted to a satellite at a determined height so that it makes a circular orbit around a planet is called orbital velocity.
• The orbital velocity of a satellite depends upon its altitude above the earth.
• The orbital speed and the distance permit the satellite to make one revolution in 24
hours.
• The orbital velocity can be calculated by the formula
 v = √GM / (R + h) where G = Gravitational constant (6.673 × 10–11Nm2 kg-2) M = Mass of the Earth (5.972 × 1024 kg) R = Radius of the Earth (6371 km) h = Height of the satellite from the surface of the Earth.

### VI. Conceptual Questions

1. Why do some stars appear blue and some red?

1. Stars appear in different colours depending on their temperatures.
2. Hot stars are white or blue in colour.
3. Cooler stars are orange or red in colour.

2. How is a satellite maintained in a nearly circular orbit?

1. The satellite is carried by a rocket to the desired height and released horizontally with a high velocity.
2. So that it remains moving in a nearly circular orbit.

3. Why are some satellites called geostationary?

The Earth rotates once in 24 hours, a satellite stays in a fixed position. Because the satellite stays over the same spot all the time, this kind of orbit is called “geostationary”.

4. A man weighing 60 kg in the Earth will weigh 1680 kg in the Sun. Why?

1. Weight of the object depends upon the gravity of the planet.
2. The gravity of the sun is 28 times higher than the Earth.
3. So an object with 60 kg in the Earth will weigh 1680 kg (28× 60 = 1680 kg) in the Sun.

### VII. Numerical Problems.

1. Calculate the speed with which a satellite moves if it is at a height of 36,000 km from the Earth’s surface and has an orbital period of 24 hr (Take R = 6370 km)

[Hint: Convert hr into seconds before doing calculation]

 r = 36000Km speed = distance/time period distance = 2πr = 2 X 3.14 X 36000 = 226080 Km. Time period = 24 hr = 86400 s Speed = 226080/86400 = 2.62 Km /s

2. At an orbital height of 400 km, find the orbital period of the satellite.

 speed , V = √(GM/(R+h)) = √ 6.673 X 10-11 X 5.972 X 1024/ (6371+400) = 0.0767 x 10 5 m/s ORBITAL PERIOD, T = 2π(R+h)/v = 2 X 3.14 X ( 6371 + 400) X 103 / 0.0767 x 105 = 5543.92 seconds

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Last Updated: 1st July 2023