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# 9th Class Chapter 5 Physics Long Questions

Dear students, prepare for physics class 9th chapter 5 long questions. These important long questions are carefully added to get you best preparation for your 9th class physics ch. 5 exams.

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##### Question: 1
Q no: 5 (A) What ismeant by the force of gravitation? Also explain the law of gravitation.
1-15
everybody in the universeattracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

According to the law of gravitation the gravitationalforce of attraction F with which the two masses m1 and m2 separated by a distance `d' attract each other is given by:
F x m1m2
F x 1/d²
F x m1m2/d²
F=G m1m2/d²
##### Question: 2
Q no(B) Define satellites. Find the orbital velocity of on artificial satellites.
2-15
Satellite:
An object that revolves around a planet is called satellite . The moon revolves around the earth as moon is a natural satellite of the earth.
Scientists have sent many objects into space Some of these objects revolve around the earth. These are called artificialsatalites. Most of the artificial satallite orbiting around the Earth are usedfor communication purposes .Artificial satellites carry instruments or passengers to perform experiments in space.
Large number of artificial satellites have been launched in different orbits around the Earth.
##### Question: 3
Q no: 6 (A) State Law of gravitation and derived the equation.
3-15
Everybody in the universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.
F x m1m2
F x 1/d²
F x m1m2/d²
F= Gm1m2/d²
##### Question: 4
Q no: 6 (B) Calculate the value of g at a height of 3600 km above the surface of the Earth.
4-15
Solution:
gn =?
h = 3600km = 3600 x 1000m
R = 6400 x 10³ m
G = 6.673 x 10-¹¹ Nm²kg-²
Me = 6x 1024 kg
g = GMe/R²
gn = Gme/(R+h)²
6.673 x10-¹¹ x 6 x 1024/6400 x10³ + 3600 x10³
gn = 4ms-²
##### Question: 5
Q no 7 (A) Explain the motion of Artificial satellites.
5-15
A satellite requires centripetal force of attraction between the salellite and the Earth provides the necessary centripetal force.
Consider a satellite of mass revolving round the earth at an altitude h in a orbit of radian to with orbital velocity Vo The necessary centripetal force required is given by equation
fc = mv²o/ro
Fc = w' = mgn
mghmv²o/ro
Vo2= gh ro
vo= √ghro
Vo= √gn(R+h)
Equation ( 5.10) gives the velocity which a satellite must possess when launched in an orbit of radius ro=9R+h) around the Earth
R+h= R
gn = g
vo=√gR
A satellite revolving around very close to the Earth has speed Vo nearly 8kms-¹ or 29000 kmh
##### Question: 6
Q no: (B) A polar satellite is launched at 850 km above earth. Find its orbital speed.
6-15
Solution:
Height= 850 km
= 850 x 1000m
850000m = 8.5 x 105m
orbital speed = v=?
V=√GMe/(R+h)
=√6.673 x 10-¹¹ x 6 x 1024/(6.4 x 106 + 8.5 x 105 )
= 743.13 ms-¹
##### Question: 7
Q no: (B) A polar satellite is launched at 850 km above earth. Find its orbital speed.
7-15
Solution:
Height= 850 km
= 850 x 1000m
850000m = 8.5 x 105m
orbital speed = v=?
V=√GMe/(R+h)
=√6.673 x 10-¹¹ x 6 x 1024/(6.4 x 106 + 8.5 x 105 )
= 743.13 ms-¹
##### Question: 8
How gravitation is discovered. what is the force of gravitation
8-15
The first man who came up with the idea of gravity was Isaac newton. It was an evening of 1665 when he was trying to solve the mystery why planets revolve around the sun. Suddenly an apple fell from the tree under which he was sitting. The idea of gravity flashed in his mind. he discovered not only the cause of falling apple but also the cause that makes the planet to revolve around the sun and the moon around the earth.
Force of gravitation: force due to which every body of the universe attracts every other body is called force of gravitation.
##### Question: 9
State and explain Newtons law of gravitation. Also derive its equation
9-15
Law of gravitation: Every object in the universe attracts every other object with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
##### Question: 10
How will you relate law of gravitation and Newtons third law of motion
10-15
in law of gravitation it is to be noted that mass m1 attracts m2 towards it with a force F while mass m2 attract m1 towards it with a force of the same magnitude F but in opposite direction. If the force acting on m1 is considered as action then the force acting on m2 will be the reaction . We can say that the action and reaction due to force of gravitation are equal in magnitude but opposite in direction. This is in consistent with newtons third law of motion which states , to every action there is always an equal but opposite reaction
##### Question: 11
State and explain gravitational field
11-15
Gravitational pull of earth acting on the body whether the body is in contact with earth or not is called the field force and the are for this force around the earth is called gravitational field
##### Question: 12
Determine the mass of earth using Newtons law of gravitation
12-15
Mass of earth: the mass of earth can be calculated by using Newtons law of gravitationExplanation; consider a body of mass m is placed on the surface of the earth. The distance between the center of the body and the earth is R which is equal to radius of the earth. The mass of earth is Me.We know that the force with which the earth attracts a body on its surface towards its center is equal to the weight of the body
##### Question: 13
What is the effect of the following on the gravitational acceleration<div><ol><li>Mass of the freely falling body</li><li>Distance of the freely falling body from the center of the earth,(I&gt;E&gt; variation of "g" with altitude0 OR explain the variation in value of 'g' with altitude</li></ol></div>
13-15
We know that
g= GMe/R2
where Me is mass of earth. Hence this equation does not include the mass of the freely fallingbody. The value of g does not depend on the mass of the body. All bodies either lighter or heavier fall freely with the same gravitationalacceleration. Thus mass has no effect on g
##### Question: 14
What do you mean by artificial satellite