NCERT Solutions for class 11 Physics | Chapter 8 - Gravitation

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Questions
1 If the mass of sun were ten times smaller and gravitational constant G were ten times larger in magnitudes
A walking on ground would become more difficult
B the acceleration due to gravity on earth will not change
C raindrops will fall much faster
D aeroplanes will have to travel much faster

Answer:A, C, D
2 Which of the following options is correct?
A acceleration due to gravity decreases with increasing altitude
B acceleration due to gravity increases with increasing depth
C acceleration due to gravity increases with increasing latitude
D acceleration due to gravity is independent of the mass of the earth

Answer:A, C
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3 If the law of gravitation, instead of being inverse-square law, becomes an inverse-cube-law
A planets will not have elliptic orbits
B circular orbits of planets is not possible
C projectile motion of a stone thrown by hand on the surface of the earth will be approximately parabolic
D there will be no gravitational force inside a spherical shell of uniform density

Answer:A, B, C
4 If the sun and the planets carried huge amounts of opposite charges,
A all three of Kepler’s laws would still be valid
B only the third law will be valid
C the second law will not change
D the first law will still be valid

Answer:A, C, D
5 Particles of masses 2M, m and M are respectively at points A, B, and C with AB = 1/2 (BC). M is much-much smaller than M and at time t = 0, they are all at rest. At subsequent times before any collision takes place

Gravitation

A m will remain at rest
B m will move towards M
C m will move towards 2M
D m will have oscillatory motion

Answer:m will move towards 2M
6 Choose the wrong option.
A inertial mass is a measure of the difficulty of accelerating a body by an external force whereas the gravitational mass is relevant in determining the gravitational force on it by an external mass
B that the gravitational mass and inertial mass are equal is an experimental result
C that the acceleration due to gravity on earth is the same for all bodies is due to the equality of gravitational mass and inertial mass
D gravitational mass of a particle-like proton can depend on the presence of neighbouring heavy objects but the inertial mass cannot

Answer:gravitational mass of a particle-like proton can depend on the presence of neighbouring heavy objects but the inertial mass cannot
7 In our solar system, the inter-planetary region has chunks of matter called asteroids. They
A will not move around the sun since they have very small masses compared to the sun
B will move in an irregular way because of their small masses and will drift away outer space
C will move around the sun in closed orbits but not obey Kepler’s laws
D will move in orbits like planets and obey Kepler’s laws

Answer:will move in orbits like planets and obey Kepler’s laws
8 Both earth and moon are subject to the gravitational force of the sun. as observed from the sun, the orbit of the moon
A will be elliptical
B will not be strictly elliptical because the total gravitational force on it is not central
C is not elliptical but will necessarily be a closed curve
D deviates considerably from being elliptical due to the influence of planets other than earth

Answer:will not be strictly elliptical because the total gravitational force on it is not central
9 Satellites orbiting the earth have a finite life and sometimes debris of satellites fall to the earth. This is because
A the solar cells and batteries in satellites run out
B the laws of gravitation predict a trajectory spiralling inwards
C of viscous forces causing the speed of the satellite and hence height to gradually decrease
D of collisions with other satellites

Answer:of viscous forces causing the speed of the satellite and hence height to gradually decrease
10 Different points in the earth are at slightly different distances from the sun and hence experience different forces due to gravitation. For a rigid body, we know that if various forces act at various points in it, the resultant motion is as if a net force acts on the cm causing translation and a net torque at the cm causing translation and a net torque at the cm causing rotation around an axis through the cm. For the earth-sun system
A the torque is zero
B the torque causes the earth to spin
C the rigid body result is not applicable since the earth is not even approximately a rigid body
D the torque causes the earth to move around the sun

Answer:the torque is zero
11 As observed from earth, the sun appears to move in an approximately circular orbit. For the motion of another planet like mercury as observed from earth, this would
A be similarly true
B not be true because the force between earth and mercury is not inverse square law
C not be true because the major gravitational force on mercury is due to sun
D not be true because mercury is influenced by forces other than gravitational forces

Answer:not be true because the major gravitational force on mercury is due to sun
12 The earth is an approximate sphere. If the interior contained matter which is not of the same density everywhere, then on the surface of the earth, the acceleration due to gravity
A will be directed towards the centre but not the same everywhere
B will have the same value everywhere but not directed towards the centre
C will be same everywhere in magnitude directed towards the centre
D cannot be zero at any point

Answer:cannot be zero at any point
13 Which of the following are true?
A A polar satellite goes around the earth’s pole in north-south direction.
B A geostationary satellite goes around the earth in east-west direction.
C A geostationary satellite goes around the earth in west-east direction.
D A polar satellite goes around the earth in east-west direction.

Answer:A, C
14 There have been suggestions that the value of the gravitational constant G becomes smaller when considered over very large time period (in billions of years) 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 sufficiently long time we will leave the solar system.

Answer:C, D
15 If the mass of sun were ten times smaller and gravitational constant G were ten times larger in magnitudes-
A walking on ground would became more difficult.
B the acceleration due to gravity on earth will not change.
C raindrops will fall much faster.
D airplanes will have to travel much faster.

Answer:A, C, D
16 If the law of gravitation, instead of being inverse-square law, becomes an inverse-cube law-
A planets will not have elliptic orbits.
B circular orbits of planets is not possible.
C projectile motion of a stone thrown by hand on the surface of the earth will be approximately parabolic.
D there will be no gravitational force inside a spherical shell of uniform density.

Answer:A, C
17 Which of the following options are correct?
A Acceleration due to gravity decreases with increasing altitude.
B Acceleration due to gravity increases with increasing depth (assume the earth to be a sphere of uniform density).
C Acceleration due to gravity increases with increasing latitude.
D Acceleration due to gravity is independent of the mass of the earth.

Answer:A, C
18 Particles of masses 2M, m and M are respectively at points A, B and C with AB = (½) (BC). m is much-much smaller than M and at time t = 0, they are all at rest (Fig. in the below).
At subsequent times before any collision takes place:

Gravitation

A m will remain at rest.
B m will move towards M.
C m will move towards 2M.
D m will have oscillatory motion.

Answer:m will move towards 2M.
19 Choose the wrong option.
A Inertial mass is a measure of difficulty of accelerating a body by an external force whereas the gravitational mass is relevant in determining the gravitational force on it by an external mass.
B That the gravitational mass and inertial mass are equal is an experimental result.
C That the acceleration due to gravity on earth is the same for all bodies is due to the equality of gravitational mass and inertial mass.
D Gravitational mass of a particle like proton can depend on the presence of neighouring heavy objects but the inertial mass cannot.

Answer:Gravitational mass of a particle like proton can depend on the presence of neighouring heavy objects but the inertial mass cannot.
20 In our solar system, the inter-planetary region has chunks of matter (much smaller in size compared to planets) called asteroids. They
A will not move around the sun since they have very small masses compared to sun.
B will move in an irregular way because of their small masses and will drift away into outer space.
C will move around the sun in closed orbits but not obey Kepler’s laws.
D will move in orbits like planets and obey Kepler’s laws.

Answer:will move in orbits like planets and obey Kepler’s laws.

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