Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

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Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Samacheer Kalvi 9th Science Universe Textbook Exercises

I. Choose the correct answer.

Question 1.
Who proposed the heliocentric model of the universe?
(a) Tycho Brahe
(b) Nicolaus Copernicus
(c) Ptolemy
(d) Archimedes
(b) Nicolaus Copernicus

Question 2.
Which of the following is not a part of outer solar system?
(a) Mercury
(b) Saturn
(c) Uranus
(d) Neptune
(a) Mercury

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 3.
Ceres is a …………..
(a) Meteor
(b) Star
(c) Planet
(d) Astroid

Question 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?
(a) 4
(b) 5
(c) 2
(d) 3
(c) 2

Question 5.
The Big Bang occurred years ago.
(a) 13.7 billion
(b) 15 million
(c) 15 billion
(d) 20 million
(a) 13.7 billion

II. Fill in the blanks.

  1. The speed of the Sun in km/s is ……………..
  2. The rotational period of the Sun near its poles is ………………..
  3. India’s first satellite is …………….
  4. The third law of Kepler is also known as the Law of ………………
  5. The number of planets in our Solar System is ………………


  1. 250
  2. 36 days
  3. Aryabhatta
  4. Harmonies
  5. 8

III. True or False.

  1. ISS is proof for international cooperation – True.
  2. Halley’s comet appears after nearly 67 hours -False.
    Correct statement: Halley’s comet appears after nearly every 76 years.
  3. Satellites nearer to the Earth should have lesser orbital velocity – False.
    Correct statement: Nearer the object to the Earth, the faster is the required orbital velocity.
  4. Mars is called the red planet – True

IV. Answer very briefly.

Question 1.
What is the solar system?

  • The Sun and celestial bodies which revolve around it form the solar system.
  • It consists of larger number of bodies such as planets, comets, asteroids and meteors.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 2.
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.

Question 3.
Define the time period of a satellite.
Time taken by the satellite to complete one revolution round the Earth is called time period of a satellite.
Time period, T = \(\frac{\text { Distance covered }}{\text { Orbital velocity }}\)

Question 4.
What is the satellite? What are the two types of satellites?
A body moving in orbit around a planet is called a satellite. The two types of satellites are natural and artificial. Earth’s natural satellite is the moon.

Question 5.
Write a note on the inner planets.

  •  The planet is relatively close together and close to the sun. They form the inner solar system and are called inner planets.
  • There are four inner planets namely
    1. Mercury, 2. Venus, 3. Earth and 4. Mars.
  • They have a surface of solid rock crust and are called terrestrial (or) rocky planets.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 6.
Write about comets in brief.
Comets are clumps 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 even seen had tails 160 million (16 crores) km long. 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.

Question 7.
State Kepler’s laws.
Kepler’s first law – the law of ellipses
The path of the planets about the Sun is elliptical in shape, with the centre of Sun being located at one of the foci.

Second law – the law of equal areas.
An imaginary line drawn from the centre of the Sun to the centre of the Planet will sweep out equal areas in equal intervals of time.

Third law – the law of Harmonics.
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.

Question 8.
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 a suitable atmosphere, and a blanket of ozone. All these have made the continuation of life possible on the Earth. The axis of rotation of the Earth is not perpendicular to the plane of its orbit. The tilt is responsible for the change of seasons on the Earth.

V. Answer in detail.

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

  • It is a Rocky planet nearest to the Sun.
  • It moves around the Sun faster than any other planet.
  • It rotates very slowly.

2. Venus

  • It is almost the same size as the Earth.
  • It is the hottest planet in our solar system.
  • It is the brightest heavenly body in our night sky.
  • It spins in the opposite direction to all other planets.

3. The Earth

  • The only Life-Supporting planet in the solar system.
  • It appears Bluish-green due to the reflection of light from water and landmass on its surface.
  • It moves around the Sun in 365.25 days and the rotation period is 23.93 hours.

4. Mars

  • The first planet outside the orbit of the Earth.
  • It is also called the Red Planet having two small natural satellites.

5. Jupiter

  • Jupiter is called a Giant planet.
  • It is the largest of all planets.
  • It has 3 rings and 65 moons.
  • Its moon Ganymede is the largest moon of our solar system.

6. Saturn

  • It has bright shiny rings and appears yellowish in colour.
  • It is the second biggest and a giant gas planet in the outer solar system.

7. Uranus

  • It is a cold gas giant and can be seen only with the help of a large telescope.
  • It has the longest summers and winters.

8. Neptune

  • It appears as a Greenish star and is the windiest planet.
  • It has the largest moon – Triton that moves in the opposite direction to the direction in which its planet spins.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 2.
Discuss the benefits of ISS.
International Space Station (ISS), is a large spacecraft which can house astronauts. It goes around in low Earth orbit at approximately 400 km distance. It is also a science laboratory. Its very first part was placed in orbit in 1998 and its core construction was completed by 2011. It is the largest man-made object in space which can also be seen from the Earth through the naked eye. The first human crew went to the ISS in 2000. Ever since that, it has never been unoccupied by humans. At any given instant, at least six humans will be present in the ISS. According to the current plan ISS will be operated until 2024, with a possible extension until 2028. After that, it could be deorbited, or recycled for future space stations.

The ISS is intended to act as a scientific laboratory and observatory. Its main purpose is to provide an international lab for conducting experiments in space, as the space environment is nearly impossible to reproduce here on Earth. The microgravity environment present in the ISS provides ideal conditions for doing many scientific types of research especially in biology, human biology, physics, astronomy and meteorology.

Question 3.
Write a note on orbital velocity.
Definition of orbital velocity :
The horizontal velocity has to be imparted to a statellite at the determined height so that it makes a circular orbit around the planet.

  1. The orbital velocity of the satellite depends on its altitude above the Earth.
  2. Nearer the object to the earth, faster is the required orbital velocity.
  3. At an altitude of 200 km, the required orbital velocity is little more than 27,400 kph.

Geostationary orbit:
Satellite stays in a fixed position all the time while earth rotates. This kind of orbit is called geostationary.

Orbital velocity formula : \(v=\sqrt{\frac{\mathrm{GM}}{(\mathrm{R}+h)}}\)
Gravitational constant (6.673 × 10-11 Nm2kg-2)

M – Mass of the Earth (5.972 × 1024kg)
R – Radius of the Earth (6371 km).
h – Height of the satellite from the surface of the Earth.

VI. Conceptual questions.

Question 1.
Why do some stars appear blue and some red?
Stars are the fundamental building blocks of galaxies. Stars were formed when the galaxies were formed during the Big Bang. Stars produce heat, light, ultraviolet rays, x-rays, and other forms of radiation. They are largely composed of gas and plasma (a superheated state of matter).

The brightness of a star depends on its intensity and the distance from the Earth. Stars also appear to be indifferent colours depending on their temperature. Hot stars are white or blue, whereas cooler stars are orange or red in colour.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

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

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

Question 3.
Why are some satellites called geostationary?
Since Earth also rotates once in 24 hours, a satellite stays in a fixed position relative to a point on Earth’s surface. Because the satellite stays over the same spot all the time, this kind of orbit is called ‘geostationary’.

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

  1. The 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.

Question 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]
T = 2π(R+h)/v
86400 = 2 × 3.14 × (6370 + 36000)/v
v = 6.28 × 42370
266083.6 km/sec
S = d/t
= 266083/24
= 11086.79 km/h

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 2.
At an orbital height of 400 km, find the orbital period of the satellite.
h = 400 × 103m, R = 6371 × 103m,
v = 7616 × 103 kms– 1.
Substituting the values,
T = 2π(R+h)/v
T = 6.28 × \(\frac { 6771 }{ 7616 }\)
T = 5.583 × 103s = 5583 .
T ≈ 93 min


Question 1.
Watch the sky in the early morning. Do you see any planet? What is its name? Find out with the help of your teachers.
The planet that can be observed in the early morning is ‘Venus’.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 2.
Prepare a list of Indian satellites from Aryabhatta to the latest along with their purposes.

Satellite Launch Date Purpose
Aryabhatta 19 April 1975 India’s first satellite.
Bhaskara-I 7 June 1979 First experimental remote sensing satellite. Carried TV and microwave cameras.
Rohini Technology Payload 10 August 1979 Intended for measuring in-flight performance of first experimental flight of SLV-3, the first Indian launch vehicle. Did not achieve orbit.
Ariane Passenger Payload Experiment 19 June 1981 First experimental communication satellite. Provided experience in building and operating a payload experiment three-axis stabilised communication satellite.
INSAT-1A 10 April 1982 First operational multipurpose communication and meteorology satellite. Procured from USA. Worked for only six months.
IRS-1A 17 March 1988 Earth observation satellite. First operational remote sensing satellite.
INSAT-2A 10 July 1992 First satellite in the second-generation Indian- built INSAT-2 series. Has enhanced capability over INSAT-1 series. Still in service.
INSAT-2E 3 April 1999 Multipurpose communication and meteorological satellite.
GSAT-1 18 April 2001 Experimental satellite for the first developmental flight of Geosynchronous Satellite Launch Vehicle, GSLV-D1.
CARTOSAT-2 10 January 2007 Advanced remote sensing satellite carrying a panchromatic camera capable of providing scene-specific spot images.
RISAT-2 20 April 2009 Radar imaging satellite used to monitor India’s borders and as part of anti-infiltration and anti-terrorist operations. Launched as a co-passenger with ANUS AT.
Oceansat-2 (IRS-P4) 23 September 2009 Gathers data for oceanographic, coastal and atmospheric applications. Continues mission of Oceansat-1.
StudSat PSLV-C15 First Indian pico-satellite (weighing less than 1 kg). Developed by a team from seven engineering colleges from Karnataka and Andhra Pradesh.              .
Jugnu 12 October 2011 Nano-satellite weighing 3 kg developed by IIT Kanpur
INSAT-3D 26 July 2013 INSAT-3D is the meteorological Satellite with advanced weather monitoring payloads.
GSAT-7 30 August 2013 GSAT-7 is the advanced multi-band communication satellite dedicated for military use.
SCATSAT-1 26 September 2016 Miniature satellite to provide weather forecasting, cyclone prediction, and tracking services to India.

Samacheer Kalvi 9th Science Universe In-Text Problems

Question 1.
Can you calculate the orbital velocity of a satellite orbiting at an altitude of 500 km?
Data: G = 6.673 × 10– 11 SI units;
M = 5.972 × 1024 kg; R = 6371000 m;
h = 500000 m.
v = \(\sqrt{\frac{6.67 \times 10^{-11} \times 5.972 \times 10^{24}}{(6371000+500000)}}\)
∴ v = 7613 ms– 1 or 7.613 kms– 1

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 2.
At an orbital height of 500 km, find the orbital period of the satellite.
h = 500 × 103m, R = 6371 × 103m,
v = 7616 × 103 kms– 1.
T = \(\frac{2 \pi(\mathrm{R}+\mathrm{h})}{\mathrm{v}}=2 \times \frac{22}{7} \times \frac{(6371+500)}{7616}\)
= 5.6677 × 103s = 5667 s.
This is T ≈ 95 min

Samacheer Kalvi 9th Science Universe Additional Questions

I. Answer the following questions.

Question 1.
What is the composition of the sun? How was it formed?
Three-quarters of the sun has hydrogen gas and one quarter has helium gas. It is over a million times as big as the earth. Hydrogen atoms combine or fuse together to form helium under enormous pressure. This process is called nuclear fusion which releases an enormous amount of energy as light and heat. It is this energy that makes sunshine and provides heat. The sun is situated at the centre of the solar system.

At the time of the Big Bang, hydrogen gas condensed to form huge clouds, which later concentrated and found numerous galaxies. Some hydrogen gas was left free in our galaxy. With time some changes occured due to which this free floating hydrogen gas concentrated and paved the way for formation of sun and the solar system.

Question 2.
What is a star? What is its composition and how was it formed?
Stars are the fundamental building blocks of galaxies. Stars were formed when the galaxies were formed during the big bang. Stars produce heat, light, ultra violet rays and other forms of radiation. They are largely composed of gas and plasma. Stars are built by hydrogen gases. Hydrogen atom fuse together to form helium atoms and in the process they produce large amount of heat.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 3.
How is the pole star distinguished from other stars? Explain.
Pole star was one of the most familiar stars for travellers in earlier times when there were no instruments or devices to find directions at night. It appears stationary because it is situated in the northern direction along the axis of rotation of the Earth.

Question 4.
What is the difference between a meteor and a meteorite?
Meteors are stony or rocky bodies scattered throughout the solar system and are very small in size. The meteors are also called shooting stars. They travel at a high speed, these pieces come closer to the Earth’s atmosphere and are attracted by the gravitational force of Earth. Some are dust particles left behind by comets and other are pieces of asteroids which have collided. These are quite small, some may be as small as a sand grain.

Meteors while travelling across the Earth’s atmosphere are fast moving and get heated up to a very high temperature by air friction. The heat produced is so high, that the meteor starts glowing and then burnt and lost. The path of the meteor appears as a streak of light in the night sky. Very large meteors are able to survive from such heat destruction and actually reach the Earth’s surface. These meteors are called meteorites.

Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

Question 5.
What is microgravity?
It is a condition in which people or objects appear to be weightless. The effects of microgravity can be seen when astronauts and objects float in space. ‘Micro’ means small, so microgravity refers to a condition where gravity is so small. Many things seem to act differently in microgravity. Fire bums differently. Without the pull of gravity, flames are mere sound.

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