# Gravitation Chapter 10 Class 9 Science Assignments

Please refer to Gravitation Chapter 10 Class 9 Science Assignments below. We have provided important questions and answers for Gravitation which is an important chapter in Class 9 Science. Students should go through the notes and also learn the solved assignment with solved questions provided below. All examination and class tests questions are as per the latest syllabus and books issued by CBSE, NCERT, and KVS. We have also provided Class 9 Science Assignments for all chapters on our website.

## Chapter 10 Gravitation Class 9 Science Assignments

Fill In The Blank

Question. The force of gravity between two objects is inversely proportional to the square of the ………..

distance between them

Question. The acceleration due to gravity at the surface of a planet depends on the ………. and the ………. of the planet.

Question. Acceleration due to gravity is ……….. proportional to the density of the planet.

directly

Question. Dimensional formula of universal gravitational constant is ………..

6M-1L3T-2@.

Question. The force of ……….. is the centripetal force on the moon.

gravity

Question. The orbit of a geostationary orbit is called ……….

parking orbit.

Question. The value of g will become 10% of its value at the earth’s surface at a height ……….. above the surface of earth. Take radius of earth as 6400 km.

57,600

Question. The weight of an object at ……….. is zero.

centre of the earth.

Question. ge and gp denotes the acceleration due to gravity on the surface of the earth and another planet whose mass and radius are twice that of the earth. The relation that holds is ………..

gp = (1 / 2) ge

Question. If the earth rotates faster, the acceleration due to gravity at equator will ………..

decreases

Question. Acceleration due to gravity ………. with depth below the surface of the earth.

decreases

Question. The constant of gravitation G is related to g by ………

g = GMe / R2

Question. Weight of an object is ………. at equator than at poles.

less

Question. If the density of planet is increased, then the acceleration due to gravity at its surface will ………..

increase

Question. ………… velocity of the planet is constant when it revolves in an elliptical orbit around the sun.

Areal

Question. Every object inside the satellite is ……….

weightless

True/False

Question. Acceleration due gravity at poles is greater than that at equator.

True

Question. Weight of body at centre of the earth is zero.

True

Question. If the earth stops rotating, acceleration due to gravity at poles increases.

False

Question. The orbit speed of a satellite is inversely proportional to radius of its orbit.

False

Question. For a spherically symmetric earth, the acceleration due to gravity should be same at the equator and at the poles

False

Question. An object in a satellite experiences weightlessness.

True

Question. If earth suddenly stops rotating about its axis, then the value of g will be same at all the places.

True

Question. Weightlessness experienced while orbiting the earth in a spaceship is the result of zero gravity.

True

Question. Force of gravity is least at the equator.

False

Question. The gravitation force between a spherical shell and a point mass inside it is negative and finite.

False

Question. It is possible to put on artificial satellite in to orbit in such a way that it will remain directly over New Delhi.

False

Question. Copernicus discovered that the earth moves around the sun.

True

Question. An astronaut cannot use a straw to sip a drink on the surface of the moon.

True

Question. Work is to be done on the system of two particles in increasing the distance between them.

True

Question. Is value of “g” same at all places on the Earth? Give reason for your answer.

No, the value of “g” is maximum at the poles and minimum at equator. This variation is because to the oblong shape of the Earth and its rotation about its own axis.

Question. Write SI unit of G.

We know F=Gm1 m2/r2
= 1 2
or G= Fr2/m1 m2
In SI system, force F is measured in N, distance r in m and masses m1 and m2 in kg, therefore
SI unit of G =Nm2/kg.kg
= = Nm2kg–2

Question. Why is G called ‘a universal gravitational constant’?

The value of G is same for any pair of objects in the universe. Also its value does not depend on the nature of the intervening medium. That is why constant G is called ‘universal gravitational constant’.

Question. What is the relation between gravitational force of the Moon with the Earth.

The gravitational force of the Moon is about one-sixth of what it is on the Earth.

Question. Name the scientist in whose honor the SI unit of pressure is named.

The SI unit of pressure is named after Blaise Pascal.

Question. Give difference between `g’ and ‘G’ in a tabular form.

Question. What is the importance of universal law of gravitation?
or
Write four phenomenons which were successfully explained using universal law of gravitation.

Many unconnected phenomenon can be explained by gravitational law successfully.
(i) Force bind us with Earth
(ii) Motion of Moon around Earth
(iii) Motion of planet around Sun
(iv) Tides due to the Moon and Sun

Match the column :

(A – 4), (B – 1), (C – 2), (D – 3)

Question.

(a) P-4, Q-1, R-2, S-3

Question.

(c) P-4, Q-1, R-2, S-3

Question.

(a) P-2, Q-4, R-3, S-1

Question.

(b) P-3, Q-4, R-1, S-2

Assertion And Reason

Direction: In each of the following questions, a statement of Assertion is given and a corresponding statement of Reason is given just below it. Of the statements, given below, mark the correct answer as:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both Assertion and Reason are false.

Question. Assertion : A man is sitting in a boat which floats on a pond. If the man drinks some water from the pond,
the level of water in the pond will decrease.
Reason : The weight of the liquid displaced by the body is greater than the weight of the body.
Answer. (d) Both Assertion and Reason are false.
Water level in the pond remains unchanged. When theman drinks water from the pond, a larger volume ofwater is displaced by the boat and hence or original water level is maintained.

Question. Assertion : At the centre of earth, a body has a centre of mass but no centre of gravity.
Reason : Acceleration due to gravity at the centre of the earth is zero.
Answer. (a) Both assertion and reason are true and reason is the correct explanation of assertion.
At the centre of the earth value of g is zero, weight of the body is also zero but its mass remains the same. The centre of mass of the body thus remains unchanged.

Question. Assertion : A block of ice with a lead shot embedded in it floats on water contained in a vessels. The temperature of the system is kept at 0cC as the ice melts. When ice has melted completely, water level in the vessel rises.
Reason : The melted ice will raise the water level.
Answer. (d) Both Assertion and Reason are false. The water level in the vessel remains unchanged. The volume or melted ice and lead shot, is equal to the volume of the water displaced when the ice block with lead shot is initially placed in water.

Question. Assertion : Kepler’s second law of planetary motion is also known as Kepler’s law of areas.
Reason : The line joining the planet and the sun sweeps equal areas in equal intervals of time.
Answer. (a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question. Assertion : During a journey from the earth to the moon and back, maximum fuel is spent to overcome the earth’s gravity at take off.
Reason : Earth’s mass is much greater than that of the moon.
Answer. (a) Both assertion and reason are true and reason is the correct explanation of assertion.
Since the earth’s mass is much more than that of the moon, the gravitational force exerted by the earth on the spaceship is much greater than that exerted by the moon. The work done is much greater.

Question. Assertion : It is the gravitational force exerted by the sun and the moon on the sea water that causes to the formation of tides in the sea.
Reason : Gravitational force of attraction is a strong force.
Answer. (c) Assertion is true but reason is false.
Gravitational force of attraction is the reason behind the formation of tides. It is a weak force.

Question. Assertion : Any two objects in the universe attract each other by a force called gravitation force.
Reason : The force of gravitation exerted by the earth is called gravity.
Answer. (b) Both assertion and reason are true but reason is not the correct explanation of assertion.

Question. Assertion : Universal gravitational constant G is a scalar quantity.
Reason : The value of G is same through out the universe.
Answer. (a) Both assertion and reason are true and reason is the correct explanation of assertion.
The value of G is independent of direction and is a constant through out the universe.

Question. Assertion : An object floats if it displaces an amount of liquid whose weight is greater than the actual weight of the object.
Reason : During floatation an object experiences no net force in the downward direction.
Answer. (b) Both assertion and reason are true but reason is not the correct explanation of assertion.
Net force = real weight – upthrust (weight of the liquid displaced).
The object rises above the liquid surface to an extent that the weight of the liquid displaced by the part of the object. Thus, an object will float when upward thrust is greater than its actual weight. (The density of the object must be less than the density of the liquid).

Question. Assertion : If we drop a stone and a sheet of paper from a balcony of first floor, then stone will reach the ground first.
Reason : The resistance due to air depends on velocity only.
Answer. (c) Assertion is true but reason is false.

Question. Assertion : The density of a liquid depends upon the nature and temperature of the liquid.
Reason : The volume of the liquid depends upon temperature.
Answer. (a) Both assertion and reason are true and reason is the correct explanation of assertion.
Density = mass/volume
The density of a liquid depends on the kind of liquid and its temperature. Volume increases with increase in temperature and vice-versa. The density decreases with increase in temperature.

Question. Assertion : When distance between two bodies is doubled and also mass of each body is doubled, then the gravitational force between them remains the same.
Reason : According to Newton’s law of gravitation, product of force is directly proportional to the product mass of bodies and inversely proportional to square of the distance between them.
Answer. (a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question. Assertion : The value of the acceleration due to gravity g on earth depends upon the average density of the earth.
Reason : It is the radius of the earth which determines the value of the g .
Answer. (b) Both assertion and reason are true but reason is not the correct explanation of assertion.
Since

,the acceleration due to gravity depends both on average density and the average radius of the earth.

Question. Assertion : The value of acceleration due to gravity changes with the height, depth and shape of the earth.
Reason : Acceleration due to gravity is zero at the centre of the earth.
Answer. (b) Both assertion and reason are true but reason is not the correct explanation of assertion.
The value of g changes with height, depth and is zero at the centre of the earth.

Question. Assertion : When the orbital radius of a planet is made 4 times, its time period increases by 8 times.
Reason : Greater the height above the earth’s surface, greater is the time period of revolution.
Answer. (b) Both assertion and reason are true but reason is not the correct explanation of assertion.
According to Kepler’s law, T 2? r3 or T ? r3/2
When r becomes four times, T is 43/2(= 23) = 8 times.

Question. Assertion : Weight of a body on earth is equal to the force with which the body is attracted towards the earth.
Reason : Weight of a body is independent of the mass of the body.
Answer. (c) Assertion is true but reason is false.

Question. Assertion : By tying a stone to a wooden plank, an object can be made such that it floats in a river and sinks in the ocean.
Reason : Density of river water is more than the density of sea-water.
Answer. (d) Both Assertion and Reason are false.
The density of sea-water is greater than the density of river water. Therefore, the buoyant force will be larger in sea-water which keeps the body float.

Question. Assertion : When a body is thrown up, the acceleration due to gravity at the topmost point is zero.
Reason : The acceleration due to gravity is always directed downwards towards the centre of the earth for a freely falling body.
Answer. (d) Assertion is false but reason is true. Acceleration due to gravity at the topmost point in case of a stone thrown upward is not zero.

Question. Assertion : An object floats on the surface of a liquid in a beaker. The whole system is allowed to fall freely under gravity. The upthrust on the object due to the liquid is equal to the weight of the liquid displaced.
Reason : Archimedes’ principle states that the upthrust on an object due to a fluid is equal to the weight of the fluid displaced.
Answer. (d) Both Assertion and Reason are false.

Question. Assertion : A sheet of paper falls slower, than one that is crumpled in to a ball?
Reason : Sheet of paper has lesser weight than that is crumpled into a ball.
Answer. (c) Assertion is true but reason is false.

Question. How does the force of gravitation between two objects change when the distance between them is reduced to half?
Answer. When the distance between the objects is reduced to half the gravitational force increases by four times the original force.

Question. The gravitational force acts on all objects in proportion to their masses. Why, then, a heavy object does not fall faster than a light object?
Answer. Acceleration due to gravity does not depend on mass of object. Hence, all bodies fall with the same acceleration provided there is no air or other resistance.

Question. What is Gravitation?
Answer. Gravitation is the force of attraction between two objects in the universe :
(i) Gravitation may be the attraction of objects by the Earth.
Example : If a body is dropped from a certain height, it falls downwards due to Earth’s gravity.
If a body is thrown upwards, it reaches a certain height and then falls downwards due to the Earth’s gravity.
(ii) Gravitation may be the attraction between objects in outer space : Attraction between the Earth and Moon. Attraction between the Sun and planets.

Question. Two objects of masses M1 and M2 are dropped in vacuum from a height above the surface of Earth (Mis greater than M2). Which one will reach the ground first and why?
Answer. Since acceleration is the rate of change of velocity, and velocity is the rate of change of position, objects dropped from the same height will feel the same acceleration, and so move with the same rate of increasing velocity, and so hit the ground at the same time, independent of their masses.

Question. Derive a relationship between “g” and “G”.
Answer. Let a body of mass m be dropped from a distance R from the centre of the Earth.
Therefore, F exerted by the Earth on the body is,
F= (G × Me × m)/R2

Where, Me is the mass of the Earth then, the acceleration of the body (a) is given by
A= Force/Mass of the body
F/m= (G × Me × m)/R2

Thus, a is independent of the mass of the object falling towards the Earth. This acceleration “a” developed by a falling object is called the acceleration due to gravity. It is denoted by “g”.
g = (G× Me)/R

Question. Why are the ends of tools like knives, pins and nails pointed?
Answer. The ends of tools such as pins, knives and nails are made pointed to increase the effect of the force.Because the pointed ends have much smaller areas.As result for a certain amount of force applied, the pressure becomes very large. That is why sharp edges needs very small force to cut fruits or vegetables.

Question. A certain particle has a weight of 30N at a place where the acceleration due to gravity is 9.8 m/s2 (a) What are its mass and weight at a place where acceleration due to gravity is 3.5 m/s square (b) What are its mass and weight at a place where acceleration due to gravity is 0?
(a) Weight of the body, W = 30, W = mg,
Mass of the body,
m =W/g = 30/3.5= 8.5 kg
New weight of the body,
W’ = mg’
= (3.06) (3.5) N = 10.71 N
(b) Mass remains the same but weight becomes zero.

Numerical Questions

Question. What is the weight of a person whose mass is 50 kg?
Answer. The weight of the person
W = mg = 50 × 9.8 = 490 N
Note : The gravitational unit of force is kg-f (kilogram force) or kg-wt (kilogram weight) 1
g – wt = 9.8 N = 1 kg-f
490 N = 50 kg-f

Question. Weight of a girl is 294 N. Find her mass.
W = mg
294 = m × 9.8
m = 30 kg

Question. Weight of an object is 294 N on the surface of the Earth. What is its weight at a height of 200 km from the surface of the Earth. Radius of the Earth = 6400 km.