Assignment - Gravitation, Class 9, Science PDF Download

MATCH THE COLUMN SINGLE COLUMN (MATRIX)

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MARK THE STATEMENT TRUE OR FALSE :
1. The force of attraction between two bodies is called gravity.
2. The value of G depends upon the mass of two objects.
3. If a spring balance, holding a heavy object is released, it will read zero weight.
4. The value of G is high if the radius of the body is more and less if radius is less.
5. The centre of mass and centre of gravity for a small body lie at the same point.
6. The gravitational force between two bodies changes if a material body is placed between them.
7. The acceleration of a body thrown up is numerically the same as the acceleration of a downward falling body but opposite is sign.
8. The value of g is zero at the centre of the earth.
9. The inertia of an object depends upon its mass.
10. All objects attract each other along the line joining their centre of mass.
11. Acceleration due to gravity, g =   where symbols have their usual meanings.
12. Relative density has no unit.
13. Archimedes' principle does not apply to gases.
14. Any solid will sink in water if its relative density is less than unity.

FILL IN THE BLANKS :

1. .................... is the force of attraction between any two bodies in the universe.

2. .................... is the force of attraction between a body and a planet.
3. Acceleration due to gravity .................... with height from the surface of the earth.
4. Acceleration due to gravity .................... with depth from the surface of the earth.
5. Acceleration due to gravity is a maximum at the ....................
6. .................... of a body changes from place to place but its .................... remains constant.
7. The upward force experienced by a body immersed partially or fully in a fluid is called ....................
8. Density of a substance is defined as the ratio of the mass of a body to its ....................
9. Relative density of a substance is defined as the ratio of the density of the substance to the density of water at ....................
10. In cgs the relative density of a substance is .................... equal to its density in gcm–3.
11. The combined weight of the sinker and cork is .................... than the weight of the sinker alone.
12. For a body to float the density of the floating object should be .................... than or equal to the density of
the liquid in which it is to float.

13. The centre of ..........is a point, where the total upthrust, due to fluid displaced by part ...........of body acts.
14. A fish .................... by squeezing out air, from its ....................
15. When a body is partly or wholly immersed in a .................... , it experience an ....................
16. An iceberg floats with .................... of its volume below ....................
17. The unit of upthrust in SI is ....................
18. Lactometer is used to measure .................... of ....................
19. A hydrometer sinks .................... in water than in pure milk.
20. The density of hot air is .................... that of cold air.

UNDERSTANDING BASE QUESTIONS :-

1. In what sense does the moon fall towards the earth ? Why does it not actually fall on the surface of earth ?
2. If the earth attracts an apple. Does the apple also attract the earth? If so, why does the earth not move towards the apple ?
3. If the force of gravity somehow vanished away, why would we sent flying in space ?
4. There are two kinds of balances, that is, a beam balance and a spring balance. If both the balances give same measure of a given body on the surface of the earth, will they give same measure on the surface of moon ? Explain your answer.
5. A bag of sugar weighs W at some place on the equator. If this bag is taken to Antarctica, will it weigh same, more or less ? Give a reason for your answer.
6. Which is greater : the attraction of Earth for 1 kg of lead or attraction of 1 kg lead for earth ?
7. The weight of a man on the earth is 100 kg. Does this weight on the moon increase or decrease ?
8. When dropped from the same height a body reaches the ground quicker at poles than at the equator. Why ?
9. What would be the effect on the weight of a body if the earth stopped rotating ?
10. A man at the top of a tower throws and object horizontally whereas he simply drops another. Will these two objects reach the earth at the same time ?
11. If gravitation is the power by which all bodies tend to towards each other, then why do all bodies tend towards the centre of the earth ?
12. What is weightlessness ?
13. Why is the bottom part of the foundation of a building made wider ?
14. Why cutting instruments are sharpened ?
15. Explain why it is difficult to push a tin can into water keeping its mouth upwards than when its mouth is kept downwards towards the water.
16. A piece of ice is gently placed on the surface of water filled in glass tumbler, so the water rises to the brim. What will happen to the level of water when the ice melts ? Will the water overflow ? If not, explain with reason.
17. You are provided with a hollow iron ball of volume 20 cm3, a mass of 15 g and a solid iron ball of mass 20 g. Both are placed on the surface of water contained in a large tub. Which will float ? Give reason for your answer.
18. Explain the following :
(i) Icebergs floating in the sea are dangerous for the ship.
(ii) An egg sinks in fresh water but floats in a strong solution of salt.
(iii) An iron nail sinks in water but a ship made of iron floats.
(iv) A ship sinks to a great depth in river water than in sea water.
(v) It is easier for a man to swim in sea water than in river water.
(vi) A dead body floats, with its head immersed in water.
19. A solid brass cylinder tied to a thread is hanging from the hook of a spring balance. The cylinder is gradually dipped into the water contained in a jar. What change do you expect in the reading of the spring balance ? Give reason for your answer.
20. If a solid of the same density as that of a liquid is placed in it, what will happen to the solid ?

HIGH ORDER THINKING SKILL QUESTIONS

1. Newton's law of gravitation is called universal law. Why ?
2. According to Newton's law of gravitation, every, particle of matter attracts every other particle. But bodies on the surface of earth never move towards each other on account of this force of attraction, why ?
3. What is the nature of motion of an object falling freely under the action of gravity ?
4. Will a body weight more on equator or on pole ?
5. Earth is continuously pulling the moon towards its centre, still it does not fall to the earth, why ?
6. How does acceleration due to gravity depend on the mass of planet ?
7. If the diameter of the earth becomes two times its present value and its mass remains unchanged, then how would the weight of an object on the surface of the earth be affected ?
8. Choose the correct alternative :
(a) Acceleration due to gravity increases/decreases with increasing altitude.
(b) Acceleration due to gravity increases/decreases with increasing depth.
(c) Acceleration due to gravity is independent of the mass of the earth/mass of the body.
9. A person can jump higher on the surface of the moon than on the earth. Why ?
10. A glass jar contains a liquid of density 'd' upto a height of 'h' at a place where acceleration due to gravity is 'g', the atmospheric pressure is PA :
(i) What is the pressure at the free surface of the liquid ?
(ii) Write an expansion for the total pressure at the base of the jar.
11. Explain why a gas bubble released at the bottom of a lake grows in size as it rises to the surface of the lake.
12. A body dipped into a liquid experiences an upthrust. State the factors on which the upthrust on the body depends.
13. Explain briefly why a balloon filled with helium gas rises in air. Why does the balloon rise to a particular height above the ground and does not rise further ?
14. Will a body weigh more in air or in vacuum when weighed with a spring balance ? Give a reason for your answer.

NUMERICAL PROBLEMS

1. What is the gravitational acceleration of a spaceship at a distance equal to two Earth's radius from the centre of the Earth?
2. A boy on a cliff 49 m high drops a stone. One second later, he throws a second stone after the ftrst. They both hit the ground at the same time. With what speed did he throw the second stone ?
3. A stone drops from the edge of the roof. It passes a window 2 m high in 0·1 s. How far is the roof above the top of the window?
4. A particle is dropped from a tower 180 m high. How long does it take to reach the ground? What is the velocity when it tourhes the ground ? Take g = 10 m/s².
5. To estimate the height of a bridge over a river, a stone is dropped freely on the river from the bridge. The stone takes 2 s to touch the water surface in the river. Calculate the height of the bridge from the water level.
Take g = 9·8 m/s².
6. How much would a 70 kg man weigh on moon? What will be his mass on Earth and Moon? Given g on Moon = 1·7 m/s².