#### Chapters

Chapter 2: Kinematics

Chapter 3: Laws of motion

Chapter 4: Work, Energy and Power

Chapter 5: Motion of System of Particles and Rigid Bodies

Chapter 6: Gravitation

Chapter 7: Properties of Matter

Chapter 8: Heat and Thermodynamics

Chapter 9: Kinetic Theory of Gases

Chapter 10: Oscillations

Chapter 11: Waves

## Chapter 6: Gravitation

### Tamil Nadu Board Samacheer Kalvi solutions for Class 11th Physics Volume 1 and 2 Answers Guide Chapter 6 Gravitation Evaluation [Pages 42 - 46]

#### Multiple Choice Questions

The linear momentum and position vector of the planet is perpendicular to each other at _________.

perihelion and aphelion

at all points

only at perihelion

no point

If the masses of the Earth and Sun suddenly double, the gravitational force between them will ___________.

remain the same

increase 2 times

increase 4 times

decrease 2 times

A planet moving along an elliptical orbit is closest to the Sun at distance r_{1} and farthest away at a distance of r_{2}. If v_{1} and v_{2} are linear speeds at these points respectively. Then the ratio `"v"_1/"v"_2` is

`"r"_2/"r"_1`

`("r"_2/"r"_1)^2`

`"r"_1/"r"_2`

`("r"_1/"r"_2)^2`

The time period of a satellite orbiting Earth in a circular orbit is independent of

Radius of the orbit

The mass of the satellite

Both the mass and radius of the orbit

Neither the mass nor the radius of its orbit

If the distance between the Earth and Sun were to be doubled from its present value, the number of days in a year would be ___________.

64.5

1032

182.5

730

According to Kepler’s second law, the radial vector to a planet from the Sun sweeps out equal areas in equal intervals of time. This law is a consequence of ___________.

conservation of linear momentum

conservation of angular momentum

conservation of energy

conservation of kinetic energy

The gravitational potential energy of the Moon with respect to Earth is ____________.

always positive

always negative

can be positive or negative

always zero

The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are K_{A}, K_{B} and K_{C} respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then

K

_{A}> K_{B}> K_{C}K

_{B}< K_{A}< K_{C}K

_{A}< K_{B}< K_{C}K

_{B}> K_{A}> K_{C}

The work done by the Sun’s gravitational force on the Earth is __________.

always zero

always positive

can be positive or negative

always negative

If the mass and radius of the Earth are both doubled, then the acceleration due to gravity g'

remains same

`"g"/2`

2 g

4 g

The magnitude of the Sun’s gravitational field as experienced by Earth is

same over the year

decreases in the month of January and increases in the month of July

decreases in the month of July and increases in the month of January

increases during day time and decreases during night time

If a person moves from Chennai to Trichy, his weight _________.

increases

decreases

remains same

increases and then decreases

An object of mass 10 kg is hanging on a spring scale which is attached to the roof of a lift. If the lift is in free fall, the reading in the spring scale is ___________.

98 N

zero

49 N

9.8 N

If the acceleration due to gravity becomes 4 times its original value, then escape speed ____________.

remains same

2 times of original value

becomes halved

4 times of original value

The kinetic energy of the satellite orbiting around the Earth is __________.

equal to potential energy

less than potential energy

greater than kinetic energy

zero

#### Short Answer Questions

State Kepler’s three laws.

State Newton’s Universal law of gravitation.

Will the angular momentum of a planet be conserved? Justify your answer.

Define the gravitational field.

Write unit of the gravitational field.

What is meant by the superposition of the gravitational field?

Define gravitational potential energy.

Is potential energy the property of a single object? Justify.

Define gravitational potential.

What is the difference between gravitational potential and gravitational potential energy?

What is meant by escape speed in the case of the Earth?

Why is the energy of a satellite (or any other planet) negative?

What are geostationary and polar satellites?

Define weight

Why is there no lunar eclipse and solar eclipse every month?

How will you prove that Earth itself is spinning?

#### Long Answer Questions

Discuss the important features of the law of gravitation.

Explain how Newton arrived at his law of gravitation from Kepler’s third law.

Explain how Newton verified his law of gravitation.

Derive the expression for gravitational potential energy.

Prove that at points near the surface of the Earth, the gravitational potential energy of the object is U = mgh.

Explain in detail the idea of weightlessness using the lift as an example.

Derive an expression for escape speed.

Explain the variation of g with latitude.

Explain the variation of g with altitude.

Explain the variation of g with depth from the Earth’s surface.

Derive the time period of the satellite orbiting the Earth.

Derive an expression for the energy of satellite.

Explain in detail the geostationary and polar satellites.

Explain how geocentric theory is replaced by heliocentric theory using the idea of retrograde motion of planets.

Explain in detail the Eratosthenes method of finding the radius of Earth.

Describe the measurement of Earth’s shadow (umbra) radius during the total lunar eclipse

#### Conceptual Questions

In the following, what are the quantities which that are conserved?

Linear momentum of planet

Angular momentum of planet

Total energy of planet

Potential energy of a planet

The work done by Sun on Earth in one year will be

Zero

Non zero

Positive

Negative

The work done by Sun on Earth at any finite interval of time is

positive, negative or zero

Strictly positive

Strictly negative

It is always zero

If a comet suddenly hits the Moon and imparts energy which is more than the total energy of the Moon, what will happen?

If the Earth’s pull on the Moon suddenly disappears, what will happen to the Moon?

If the Earth has no tilt, what happens to the seasons of the Earth?

A student was asked a question ‘why are there summer and winter for us? He replied as ‘since Earth is orbiting in an elliptical orbit, when the Earth is very far away from the Sun (aphelion) there will be winter, when the Earth is nearer to the Sun (perihelion) there will be winter’. Is this answer correct? If not, what is the correct explanation for the occurrence of summer and winter?

The following photographs are taken from the recent lunar eclipse which occurred on January 31, 2018. Is it possible to prove that Earth is a sphere from these photographs?

#### Numerical Problems

An unknown planet orbits the Sun with a distance twice the semi-major axis distance of the Earth’s orbit. If the Earth’s time period is T_{1}, what is the time period of this unknown planet?

Assume that you are in another solar system and provided with the set of data given below consisting of the planets’ semi-major axes and time periods. Can you infer the relation connecting semi-major axis and time period?

Planet (imaginary) |
Time period (T) (in year) |
Semi-major axis (a) (in AU) |

Kurinji | 2 | 8 |

Mullai | 3 | 18 |

Marutham | 4 | 32 |

Neithal | 5 | 50 |

Paalai | 6 | 72 |

If the masses and mutual distance between the two objects are doubled, what is the change in the gravitational force between them?

Two bodies of masses m and 4m are placed at a distance of r. Calculate the gravitational potential at a point on the line joining them where the gravitational field is zero.

If the ratio of the orbital distance of two planets `"d"_1/"d"_2` = 2, what is the ratio of gravitational field experienced by these two planets?

The Moon I_{o} orbits Jupiter once in 1.769 days. The orbital radius of the Moon I_{o} is 421700 km. Calculate the mass of Jupiter?

If the angular momentum of a planet is given by `vec"L" = 5"t"^2hat"i" - 6"t"hat"j" + 3hat"k"`. What is the torque experienced by the planet? Will the torque be in the same direction as that of the angular momentum?

Four particles, each of mass M and equidistant from each other, move along a circle of radius R under the action of their mutual gravitational attraction. Calculate the speed of each particle.

Suppose unknowingly you wrote the universal gravitational constant value as G = 6.67 × 10^{11}. instead of the correct value, G = 6.67 × 10^{−11}, what is the acceleration due to gravity g' for this incorrect G? According to this new acceleration due to gravity, what will be your weight W'?

Calculate the gravitational field at point O due to three masses m_{1}, m_{2} and m_{3} whose positions are given by the following figure. If the masses m_{1} and m_{2} are equal what is the change in a gravitational field at the point O?

What is the gravitational potential energy of the Earth and Sun? The Earth to Sun distance is around 150 million km. The mass of the Earth is 5.9 × 10^{24 }kg and the mass of the Sun is 1.9 × 10^{30} kg.

Earth revolves around the Sun at 30 km s^{−1}. Calculate the kinetic energy of the Earth. In the previous example, you calculated the potential energy of the Earth. What is the total energy of the Earth in that case? Is the total energy positive? Give reasons.

An object is thrown from Earth in such a way that it reaches a point at infinity with non-zero kinetic energy `["K"."E"("r" = ∞) = 1/2 "Mv"_"∞"^2]`, with what velocity should the object be thrown from Earth?

Suppose we go 200 km above and below the surface of the Earth, what are the g values at these two points? In which case, is the value of g small?

Calculate the change in g value in your district of Tamil nadu. (Hint: Get the latitude of your district of Tamil nadu from Google). What is the difference in g values at Chennai and Kanyakumari?

## Chapter 6: Gravitation

## Tamil Nadu Board Samacheer Kalvi solutions for Class 11th Physics Volume 1 and 2 Answers Guide chapter 6 - Gravitation

Tamil Nadu Board Samacheer Kalvi solutions for Class 11th Physics Volume 1 and 2 Answers Guide chapter 6 (Gravitation) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the Tamil Nadu Board of Secondary Education Class 11th Physics Volume 1 and 2 Answers Guide solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Class 11th Physics Volume 1 and 2 Answers Guide chapter 6 Gravitation are Gravitational Field and Gravitational Potential, Escape Speed and Orbital Speed, Elementary Ideas of Astronomy, Introduction to Gravitation, Acceleration Due to Gravity of the Earth.

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