Universe Book Back Questions 9th Science Lesson 9

9th Science Lesson 9

9] Universe

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

The distance of Andromeda, our nearest galaxy is approximately 2.5 million light-years. If we move at the speed of the Earth (30 km/s), it would take us 25 billion years to reach it!

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.

Problem 1: Can you calculate the orbital velocity of a satellite orbiting at an altitude of 500 km? Data: G = 6.673 x 10^-11 SI units; M = 5.972 x 10²⁴ kg; R = 6371000 m; h = 500000 m.

Solution: v = √6.67 x 10^-11 x 5.972 x 10²⁴/(6371000 + 500000)

Ans: v = 7613 ms^-1 or 7.613 kms^-1

Microgravity is the 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 very small, so microgravity refers to the condition where gravity ‘seems’ to be very small.

Problem 2: At an orbital height of 500 km, find the orbital period of the satellite.

Solution: h = 500 x 10³m, R = 3671 x 10³ m, v = 7616 x 10³ kms^-1.

T = 2π(R + h) /v = 2 x 22/7 x (6371 + 500) /7616 = 5.6677 x 10³ s = 5667 s.

This is T ≈ 95 min

All stars appear to us as moving from east to west, where as there is one star which appears to us stationary in its position. It has been names as Pole star. The pole star appears to us as fixed in space at the same place in the sky in the north direction because it lies on the axis of rotation of the Earth which itself is fixed and does not change its position in space. It may be noted that the pole star is not visible from the southern hemisphere.

Choose the best answers:

1. Who proposed the heliocentric model of the universe?

(a) Tycho Brahe

(b) Nicolaus Copernicus

(c) Ptolemy

(d) Archimedes

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

(a) Mercury

(b) Saturn

(c) Uranus

(d) Neptune

3. Ceres is a ________________

(a) Meteor

(b) Star

(c) Planet

(d) 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?

(a) 4

(b) 5

(c) 2

(d) 3

5. The Big Bang occurred _______________ year ago.

(a) 13.7 billion

(b) 15 million

(c) 15 billion

(d) 20 million

Fill in the blanks:

1. The speed of 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 _____________.

State true or false. If false, correct the statement:

1. ISS is a proof for international cooperation.

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

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

4. Mars is called the red planet.

Answers:

Choose the best answers:

1. Nicolaus Copernicus 2. Mercury 3. Asteroid 4. 2 5. 13.7 billion

Fill in the blanks:

1. 250 2. 36 days 3. Aryabhatta 4. Harmonies 5.8

State true or false. If false, correct the statement:

1.True

2.False

Correct answer: Halley’s comet appears after nearly 76 years

3.False

Correct answer: Nearer the object to the earth, the faster is the required orbital velocity

4.True