NCERT Exemplar Solution Class 9 Science Chapter 10
NCERT Exemplar Solution Class 9 Science Chapter 10 Gravitation all Questions Answer Solution. NCERT Exemplar Class 9 Science Chapter 10 Solution PDF.
NCERT Exemplar Solution Class 9 Science Chapter 10: Overview
NCERT Exemplar Solution Class 9 Science Chapter 10 |
|
Board |
NCERT |
Topic |
Exemplar Problem Solution |
Class |
9 |
Subject |
Science |
Chapter |
10 |
Chapter Name |
Gravitation |
NCERT Exemplar Solution Class 9 Science Chapter 10 Gravitation
Chapter10
GRAVITATION
Multiple Choice Questions
1) Two objects of different masses Falling freely near the surface of moon would
a) Have same velocities at any instant
b) Have different accelerations
c) Experience forces of same magnitude
d) Undergo a change in their inertia
Answer:- a) have same velocities at any instant.
Mass does not affect the acceleration of the object. It is dependent over the acceleration due to gravity. Thus all the object falling freely will have same velocities.
2) The value of acceleration due to gravity
a) Is same on equator and poles
b) Is least on poles.
c) Is least in equator
d) Increases from pole to equator
Answer:- c) is least in equator
Equator has the more distance from its surface to the centre. But the poles has the less distance thus poles has higher acceleration due to gravity. And the equator has the least value of acceleration due to gravity.
3) The gravitational force between two objects is F. If masses of both objects are halved without changing distance between them, then the gravitational force would become
a) F/4
b) F/2
c) F
d) 2F
Answer:- a) F/4
Gravitational force will become 4th part of the gravitational force between. Two objects.
4) A boy is whirling a stone tied with a string in an horizontal circular path. If the string breaks, the stone
a) Will continue to move in the circular path
b) Will move along a straight line towards the centre of the circular path
c) Will move along a straight line tangential to the circular path
d) Will move along a straight line perpendicular to the circular path away from the boy.
Answer:-d) will move along a straight line
When an object moves along with centripetal motion and suddenly the string breaks then the object will move along the straight line from where the circular motion stops.
5) An object is put one by one in three liquids having different densities. The object floats with 1/9, 2/11, and 3/7 parts of their volumes outside the liquid surface in liquids of densities d 1, d 2, and d3respectively. Which of the following statements is correct?
a) d1> d2> d3
b) d1>d2<d3
c) d1<d2>d3
d) d1<d2<d3
Answer:- d) d1<d2<d3
Density of 1st object is Larger than 2nd object than the 3rd one.
6) In the relation F = G M m/d2, the quantity G
a) Depends on the value of g at the place of observation
b) Is used only when the earth is one of the two masses
c) Is greatest at the surface of the earth
d) Is universal constant of nature
Answer:- d) is universal constant of nature.
The quantity of G is the universal constant of nature. G is known as the force of gravity exerting on every body. It is also known as Newton’s constant.
7) Law of gravitation gives the gravitational force between
a) The earth and a point mass only
b) The earth and sun only
c) Any two bodies having some mass
d) Two charged bodies only
Answer:- c) Any two bodies having some mass.
The law of gravitation states the gravitational force between the any two bodies having some mass. It does not states only the gravitational force between the earth and sun, or earth and point mass or any charge body.
8) The value of quantity G in the law of gravitation
a) Depends on mass of earth only
b) Depends on radius of earth only
c) Depends on both mass and radius of earth
d) Is independent of mass and radius of the earth.
Answer:- d) is independent of mass and radius of the earth.
The value of quantity of G in the law of gravitation is independent of mass and radius of the earth, because it is an universal constant. Which is also known as Newton’s constant.
9) Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance between them unchanged, the value of gravitational force between them will be
a) ¼ times
b) 4 times
c) ½ times
d) Unchanged
Answer:- b) 4 times
The value of the gravitational force will be 4 times if the mass of two particles is doubled. It can be derived using the formula F = G × m1×m2/ r2
10) The atmosphere is held to the earth by
a) Gravity
b) Wind
c) Clouds
d) Earth’s magnetic field
Answer:- a) gravity
Our earth has atmosphere Which is bound by the gravitational force of earth. Wind and clouds are the part of atmosphere. And the earth’s magnetic filed does not play the role in the helding of atmosphere.
11) The force of attraction between two unit point masses separated by a unit distance is called
a) Gravitational potential
b) Acceleration due to gravity
c) Gravitational filed
d) Universal gravitational constant
Answer:- d) universal gravitational constant
G is also a universal gravitational constant it is also called as Newton’s constant.
12) The weight of an object at the centre of the earth of radius R is
a) Zero
b) Infinite
c) R times the weight at the surface of the earth’
d) 1/R2times the weight at weight at surface of the earth’
Answer:- a) zero
The weight of an object at the centre of the earth of Radius R will be zero because weight = mass × gravity. Gravity is zero at the centre. Thus weight is zero.
13) An object weighs 10 N in air. When immersed fully in water, if weighs only 8 N. The weight of the liquid displaced by the object will be
a) 2 N
b) 8 N
c) 10 N
d) 12 N
Answer:- a) 2N
The weight of the liquid displaced by the object will be 2 N.
Weight in air = 10 N
Weight in liquid = 8 N
Now,
The weight display by the object = =weight in air – weight in liquid
= 10 N – 8 N = 2 N
14) A girl stands on a box having 60 cm length, 40 cm breadth and 20 cm width in three ways. In which of the following cases, pressure exerted by the brick will be
a) Maximum when length and breadth from the base
b) Maximum when breadth and width from the base
c) Maximum when width and length form the base
d) The same in all the above three cases
Answer:- b) maximum when breadth and width from the base
The pressure exerted by the brick will be maximum when breadth and width from the base because the pressure is inversely proportional to the area. The smaller the area the greater the pressure.
15) The apple falls from a tree because of gravitational attraction between the earth and apple. If F1is the magnitude of force exerted on the earth on the apple and F2 is the magnitude of force exerted by Apple on earth, then
a) F1 is very much greater than F2
b) F2 is very much greater than F1
c) F1 is only a little greater than F2
d) F1 and F2 are equal
Answer:- d) F1 and F2 are equal
F1 and F2 will be same or equal because every action has an equal and opposite reaction according to 3rd low of motion.
Short Answer Questions
16) What is the source of centripetal force that a planet requires to revolve around the sun? On what factors does that force depend?
Answer:- To revolve around the sun centripetal force us necessary. Here the source of centripetal force is the gravitational force. Which helps the planets to revolve in centripetal force around the sun.
17) On the earth, a stone is thrown from a height in a direction parallel to the earth’s surface while another stone is simultaneously dropped from the same height. Which stone would reach the ground first and why?
Answer:- Both the stones will react he ground at the same as these are thrown simultaneously from the same height.
18) Suppose gravity of earth suddenly becomes zero, then in which direction will the moon begin to move if no other celestial body affects it?
Answer:- Moon rotates along the earth in centripetal force which requires the gravitational force. If the gravitational force suddenly becomes zero, then the moon will not rotate around the earth, immediately it will start moving in straight line from that point.
19) Identical packets are dropped from two aeroplanes, one above the equator and the other above the north pole, both at height h. Assuming all conditions are identical, will those packets take same time to reach the surface of earth. Justify your answer.
Answer:- No. Both the packets will not reach the surface at the same time. Although they are identical but these are dropped one from equator and another from pole. The gravity value at the equator of earth is less than the pole of earth. Thus, the packet fall from the equator will reach late to the surface than the packet fall from the pole of the earth.
20) The weight of any person on the moon is about 1/6 times that on the earth. He can lift a mass of 15 kg on the earth. What will be the maximum mass, which can be lifted by the same force applied by the person on the moon?
Answer:- Max. Mass lifted by the person over the moon= ?
So, Here we take,
Gravitational force over the earth (ge)= g
Gravitational force over the moon (gm)= g/6
Force needs to lift 15 kg over the earth=
F = m ge
F = 15 N
The force over the earth and over the moon will be the same.
Now
The max mass can be lift by the person over the moon with 15 N force
m = F/gm
15 g
m= –––––
g/6
m= 90 kg.
Therefore, the maximum mass can be life by the person over the moon is 90 kg.
22) The earth is acted upon by gravitation of sun, even though it does not fall into the sun. Why?
Answer:- Earth revolves around the sun in the centripetal manner. These required centripetal force is provide by the gravitational force of the sun. And thus the sun revolves in the circular path Therefore it does not fall over the sun.
Long Answer Questions
23) How does the weight of an object vary with respect to mass and results of the earth. In a hypothetical case, if the diameter of the earth’ becomes half of its present value and it’s mass becomes four times of its present value, then how would the weight of any object on the surface of the earth be affected?
Answer:- Let,
Mass of the earth be = M
Radius of the earth be = R
Now,
Weight of the body is directly proportional to mass of the earth and also it is inversely proportional to the square of the radius of earth.
Real weight
Wo =mG × M/R2 –––equation (1)
When the weight changed 4 times more it becomes 4M and radius is changed to R/2
And the new weight becomes
W* = mG× 4m/(R/2)2
W* = 16 (m G × M/R 2 )
W* = 16 × Wo ———-(from equation 1)
Thus the new weight becomes 16 times more than the original weight.
24) How does the force of attraction between the two bodies depend upon their masses and distance between them ? A student thought that two bricks tied together would fall faster than a single one under the action of gravity. Do you agree with his hypothesis or not? Comment.
Answer:- F Type equation here. Force is Directly proportional to the m1 and m2, and it is inversely proportional to square of the distance. These is the relationship between force of attraction, mass and direction. And the given hypothesis that the two bricks tied together would fall faster than a single one under the action of gravity is not correct. It will be possible if the bricks are not tied and fall freely.
25) Two objects of masses m1, and m2 having the same size are dropped simultaneously from heights h1 and h2 respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if (i) one of the objects is hollow and the other one is solid and (ii) both of them are hollow, size remaining the same in each case. Give reason.
Answer:- We have given the information,
If x= 0 then,
h1 = ½ g(t1)2
h2 = ½ g (t2)2
Now, the ratio between them
t1 / t2 = √h1 / √h2
The ratio of time and height will not change in any condition because the acceleration is the same, acceleration does not depend upon the mass and size in the case of free fall.
26) A) A cube of side 5 cm is immersed in water and then in saturated salt solution. In which case will it experience a greater buoyant force. If each side of the effect on the buoyant force experienced by the cube as compared to the first case for water. Give reason for each case.
Answer:- If an cube is immersed in water and saturated salt solution then the cube will experience greater buoyant force in the saturated salt solution.
These is because the water has less density than the saturated salt solution thus in water cube will experience less buoyant force than the salt solution.
The first cube will experience greater buoyant force than the second one. Because second cube has less volume than the first cube so it will experience less buoyant force than the first one.
B) A ball weighing 4 kg of density 4000 kg m-3is completely immersed in water of density 103 kg m-3 find the force of buoyancy on it. (Given g= 10 m s-2)
Answer:-
Given :-
g = 10 m s-2
Ball Density = 4000 kg m-3
Weight = 4 kg
Water density = 103kg m-3
Force of buoyancy =?
Now here,
Buyout force = density of water × volume of water displace × g
Buyout force = 1000 × 4 /4000 × 10
Buyout force = 10 N.
Here is your solution of NCERT Exemplar Solution Class 9 Science Chapter 10 Gravitation .
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