### Question:

The earth is acted upon by gravitation of Sun, even though it does not fall into the Sun. Why ?

#### Answer:

The earth does not fall into the sun due to gravitational pull of sun on earth.This is because earth is not stationary.It is revolving around the sun in a particular orbit.The centripetal force required by the earth for revolution around the sun is provided by gravitational pull of sun on the earth. In other words, gravitation pull of sun on earth is spent up in providing necessary centripetal force required by the earth for revolution around the sun. Hence the earth does not fall into the sun.

### Gravitation

#### Q 1.

A cuboid room has dimensions 50m x 15m x 3.5m. What is the mass of the air enclosed in the room if the density of air = 1.30 kg/m

^{3}.

#### Q 2.

How is gravitational force of attraction between two bodies affected if(i) Mass of both bodies is doubled.(ii) Distance between them is halved.

#### Q 3.

What do you mean by Thrust or Buoyant force?

#### Q 5.

Why does a block of plastic released under water come up to the surface of the water?

#### Q 6.

Relative density of silver is 10.8. If the density of water is 10

^{3}kg/m

^{3}, find density of silver.

#### Q 7.

A solid weighs 80g in air, 64g in water. Calculate the relative density of solid.

#### Q 8.

Define weight? How it is related to mass?

#### Q 9.

Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s

^{2}.)

#### Q 10.

A ball is thrown upwards from the ground of a tower with a speed of 20 m/s. There is a window in the tower at the height of 15m from ground. How many times and when will the ball pass the window? (g = 10 m/s

^{2})

#### Q 11.

In what direction does the buoyant force on an object immersed in a liquid act?

#### Q 12.

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

#### Q 13.

Fill in the blanks :

The value of

**g** ________ (increases/decreases) as we go upwards from the earth's surface.

#### Q 14.

State the universal law of gravitation.

#### Q 15.

What happens to the force between two objects, if(i) the mass of one object is doubled? (ii) the distance between the objects is doubled and tripled?(iii) the masses of both objects are doubled?

#### Q 16.

(a) What is the relationship between g and G?

(b) Show mathematically whether g (acceleration due to gravity on the earth) depends on the mass of the object itself or not.

(c) Show that for a given location on the surface of the earth g is almost constant.

#### Q 17.

How does value of 'g' vary on the earth? What are the factors responsible for this?

#### Q 19.

Write the standard equations of motion when an object is thrown upwards with some initial velocity?

#### Q 20.

A ball is thrown with some velocity 'u' m/s. Show that under free fall, it will fall the ground with same velocity.

#### Q 22.

Name the scientist who identified the relation about force of gravitation. Name the law.

#### Q 23.

Why does one feel giddy while moving on a merry go round ?

#### Q 24.

Fill in the blanks :

Motion of body with constant speed in a circular path is called ______________.

#### Q 25.

Fill in the blanks :

Assuming negligible air drag, if a steel ball and a table tennis ball are dropped from a height of 100 metres, both will reach the ground at ________ time(s). (same/different)

#### Q 26.

A ball of mass 4kg and density 4000 kgm

^{3} is completely immersed in water. Find the buoyant force acting on ball if the density of water is 10

^{3}kg/m

^{3}. (Take g = 10ms

^{-2})

#### Q 27.

Fill in the blanks :

When objects of different masses and sizes are dropped from same height would reach the ground at ______ (same time/different times), considering negligible air resistance.

#### Q 28.

Fill in the blanks :

The SI unit of weight is _____.

#### Q 29.

An object moves in a circular motion due to centripetal force, acting towards the center. The moon also rotates around the earth? Does centripetal force acts on it? Why does the moon not fall on the earth?

OR

Q:If the moon attracts the earth, why does the earth not move towards the moon?

#### Q 30.

How gravitational force is different from or similar to magnetic force (between two magnets) or coulomb force (between two charged object)?

#### Q 31.

Is weight a scalar quantity?

#### Q 32.

Fill in the blanks :

The SI unit of mass is ______.

#### Q 33.

State Archimedesâ€™ Principle. Based on this principle, write its two applications.

#### Q 34.

Is the Archimedes principle applicable to gases?

#### Q 35.

A force of 200 N acts on a surface of area 10 cm

^{2}. Calculate thrust and pressure. How much the pressure changes if the area of contact increases to 50 cm

^{2}.

#### Q 36.

Fill in the blanks :

Geocentric model i.e. the Earth is the orbital centre of all celestial bodies was proposed by _____.

#### Q 37.

Gravitational force on the surface of the moon is only 1/6th as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth? What is the value of 'g' at the surface of the moon?

#### Q 38.

Is acceleration due to gravity a vector or a scalar? Write its S.I. unit.

#### Q 39.

A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate(i) the maximum height to which it rises.(ii)the total time it takes to return to the surface of the earth.

#### Q 40.

A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.

#### Q 41.

Is mass a scalar quantity?

#### Q 42.

Fill in the blanks :

A body is said to be in _______ when only gravity acts on it.

#### Q 43.

Fill in the blanks :

The SI unit of weight is _______.

#### Q 44.

Fill in the blanks :

All other variables remaining constant, the force of gravitation is ________ proportional to the square of distance between the two objects.

#### Q 45.

The weight of a man is 690N which contains 5.3 x 10

^{-3} m

^{3} of blood. Find (a) blood's weight. Take density of blood is 1060 kg/m

^{3} (b) express it as a percentage of body weight.

#### Q 46.

Why does an object float or sink when placed on the surface of the water?

#### Q 47.

Loaded test-tube placed in pure milk sinks to a certain mark (M). Now some water is mixed with the milk. Will the test tube sink more or less? Explain.

#### Q 48.

Fill in the blanks :

The mass of the earth is ________ kg.

#### Q 49.

What was geocentric model? Who proposed this theory?

#### Q 50.

What is retrograde motion of planets (say mars planet)?