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NCERT Solutions for class 11 Physics | Chapter 8 - Gravitation

Questions
1 Choose the factor on which the orbital velocity does not depend when the satellite is orbiting close to the earth’s surface
A The mass of the earth
B The mass of the satellite
C The orbital radius
D The radius of the earth

Answer:The mass of the satellite
2 What happens to the gravitational potential at the centre of the uniform spherical shell which shrinks gradually?
A Remains constant
B Decreases
C Increases
D Oscillates

Answer:Decreases
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3 What is rotational period of a geostationary satellite?
A 6 hours.
B 12 hours.
C 48 hours.
D 24 hours.

Answer:24 hours.
4 Kepler’s second law of constancy show the conservation of which of these following?
A Angular momentum.
B Linear momentum.
C Energy.
D None of the above.

Answer:Angular momentum.
5 What is energy required to move a body of mass m from an orbit with radius 2R to 3R?
A GmM/12R^2
B GmM/8R
C GmM/6R
D GmM/2R^2

Answer:GmM/6R
6 What is ratio of linear velocities v1 and v2 of two planets which are at a distance closest and farthest from the sun? Distance from closest planet and farthest planet are d1 and d2 respectively.
A (d1/d2)^2
B (d2/d1)
C (d1/d2)
D (d1/d2)^2

Answer:(d2/d1)
7 Orbital velocity of a satellite is dependent on which factor when it is orbiting near the earth’s surface?
A Mass of the satellite.
B Mass of earth.
C Radius of earth.
D Orbital radius.

Answer:Radius of earth.
8 Gravitational mass of a body is proportional to the gravitational of what?
A Field.
B Intensity.
C Force.
D All the above.

Answer:All the above.
9 What is the kinetic energy of a satellite taking time T for revolution?
A 1/T
B T^(-2/3)
C 1/T^2
D 1/T^3

Answer:T^(-2/3)
10 Which of the following proves there is a gravitational force between the earth and the sun?
A Occurrence of day and night.
B Earth revolving around the sun.
C Sun apparently revolving around the earth.
D Falling bodies deviating towards the east.

Answer:Earth revolving around the sun.
11 The distance between two masses is doubled, what happens to the gravitational force between them?
A Double
B Half
C Remains same
D Decreased to a quarter

Answer:Decreased to a quarter
12 The earth and the moon are subjected to the sun’s gravitational force. What does the orbit of the moon look like from the sun?
A Elliptical.
B Somewhat elliptical.
C Parabola.
D Hyperbola.

Answer:Somewhat elliptical.
13 What is the weight of a body at the earth’s centre?
A Zero.
B Same as on the surface of the earth.
C Less than the weight on the earth’s surface.
D None of the above.

Answer:Zero.
14 If the gravitation effect were to be lesser than this present effect, which other force would likely to have altered?
A Electrostatic force.
B Archimedes principle.
C Viscous effect.
D None of these.

Answer:Archimedes principle.
15 What holds the atmosphere to earth?
A Gravity
B Clouds
C Winds
D None of the above

Answer:Gravity
16 What causes tidal waves in the sea?
A Gravitation effect on the earth by moon.
B Gravitational effect on the earth by the sun.
C The atmospheric impact of earth.
D None of these.

Answer:Gravitation effect on the earth by moon.
17 Supposing Newton’s law of gravitation for gravitation forces F1 and F2 between two masses m1 and m2 at positions r1 and r2 read

Gravitation

where Mo is a constant of the dimension of mass, r12 = r1 – r2 and n is a number. In such a case,

A the acceleration due to gravity on earth will be different for different object
B none of the three laws of Kepler will be valid
C only the third law will become invalid
D for n negative, an object lighter than water will sink in water

Answer:A, C, D
18 The centre of mass of an extended body on the surface of the earth and its centre of gravity
A are always at the same point for any size of the body
B are always at the same point only for spherical bodies
C can never be at the same point
D is close to each other for objects, say of sizes less than 100 m

Answer:is close to each other for objects, say of sizes less than 100 m
19 Which of the following are true?
A a polar satellite goes around the earth’s pole in a north-south direction
B a geostationary satellite goes around the earth in an east-west direction
C a geostationary satellite goes around the earth in a west-east direction
D a polar satellite goes around the earth in an east-west direction

Answer:A, C
20 There have been suggestions that the value of the gravitational constant G becomes smaller when considered over a very large time period in the future. If that happens for our earth,
A nothing will change
B we will become hotter after billions of years
C we will be going around but not strictly in closed orbits
D after a sufficiently long time we will leave the solar system

Answer:C, D

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