Tamil Nadu Board of Secondary EducationHSC Science Class 11th

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

## Chapter 6: Gravitation

Evaluation
Evaluation [Pages 42 - 46]

### 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

Evaluation | Q I. 1. | Page 42

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

Evaluation | Q I. 2. | Page 42

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

Evaluation | Q I. 3. | Page 42

A planet moving along an elliptical orbit is closest to the Sun at distance r1 and farthest away at a distance of r2. If v1 and v2 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

Evaluation | Q I. 4. | Page 42

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

• The mass of the satellite

• Both the mass and radius of the orbit

• Neither the mass nor the radius of its orbit

Evaluation | Q I. 5. | Page 42

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

Evaluation | Q I. 6. | Page 42

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

Evaluation | Q I. 7. | Page 42

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

• always positive

• always negative

• can be positive or negative

• always zero

Evaluation | Q I. 8. | Page 42

The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are KA, KB and KC 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

• KA > KB > KC

• KB < KA < KC

• KA < KB < KC

• KB > KA > KC

Evaluation | Q I. 9. | Page 43

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

• always zero

• always positive

• can be positive or negative

• always negative

Evaluation | Q I. 10. | Page 43

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

Evaluation | Q I. 11. | Page 43

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

Evaluation | Q I. 12. | Page 43

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

• increases

• decreases

• remains same

• increases and then decreases

Evaluation | Q I. 13. | Page 43

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

Evaluation | Q I. 14. | Page 43

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

Evaluation | Q I. 15. | Page 43

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

• equal to potential energy

• less than potential energy

• greater than kinetic energy

• zero

Evaluation | Q II. 1. | Page 43

State Kepler’s three laws.

Evaluation | Q II. 2. | Page 43

State Newton’s Universal law of gravitation.

Evaluation | Q II. 3. | Page 43

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

Evaluation | Q II. 4. | Page 43

Define the gravitational field.

Evaluation | Q II. 4. | Page 43

Write unit of the gravitational field.

Evaluation | Q II. 5. | Page 43

What is meant by the superposition of the gravitational field?

Evaluation | Q II. 6. | Page 43

Define gravitational potential energy.

Evaluation | Q II. 7. | Page 43

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

Evaluation | Q II. 8. | Page 42

Define gravitational potential.

Evaluation | Q II. 9. | Page 43

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

Evaluation | Q II. 10. | Page 43

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

Evaluation | Q II. 11. | Page 43

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

Evaluation | Q II. 12. | Page 43

What are geostationary and polar satellites?

Evaluation | Q II. 13. | Page 43

Define weight

Evaluation | Q II. 14. | Page 44

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

Evaluation | Q II. 15. | Page 44

How will you prove that Earth itself is spinning?

Evaluation | Q III. 1. | Page 44

Discuss the important features of the law of gravitation.

Evaluation | Q III. 2. | Page 44

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

Evaluation | Q III. 3. | Page 44

Explain how Newton verified his law of gravitation.

Evaluation | Q III. 4. | Page 44

Derive the expression for gravitational potential energy.

Evaluation | Q III. 5. | Page 44

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

Evaluation | Q III. 6. | Page 44

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

Evaluation | Q III. 7. | Page 44

Derive an expression for escape speed.

Evaluation | Q III. 8. | Page 44

Explain the variation of g with latitude.

Evaluation | Q III. 9. | Page 44

Explain the variation of g with altitude.

Evaluation | Q III. 10. | Page 44

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

Evaluation | Q III. 11. | Page 44

Derive the time period of the satellite orbiting the Earth.

Evaluation | Q III. 12. | Page 44

Derive an expression for the energy of satellite.

Evaluation | Q III. 13. | Page 44

Explain in detail the geostationary and polar satellites.

Evaluation | Q III. 14. | Page 44

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

Evaluation | Q III. 15. | Page 44

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

Evaluation | Q III. 16. | Page 44

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

#### Conceptual Questions

Evaluation | Q IV. 1. | Page 44

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

Evaluation | Q IV. 2. | Page 44

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

• Zero

• Non zero

• Positive

• Negative

Evaluation | Q IV. 3. | Page 44

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

Evaluation | Q IV. 4. | Page 44

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

Evaluation | Q IV. 5. | Page 44

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

Evaluation | Q IV. 6. | Page 44

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

Evaluation | Q IV. 7. | Page 44

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?

Evaluation | Q IV. 8. | Page 45

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

Evaluation | Q V. 1. | Page 45

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 T1, what is the time period of this unknown planet?

Evaluation | Q V. 2. | Page 45

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
Evaluation | Q V. 3. | Page 45

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

Evaluation | Q V. 4. | Page 45

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.

Evaluation | Q V. 5. | Page 45

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?

Evaluation | Q V. 6. | Page 45

The Moon Io orbits Jupiter once in 1.769 days. The orbital radius of the Moon Io is 421700 km. Calculate the mass of Jupiter?

Evaluation | Q V. 7. | Page 45

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?

Evaluation | Q V. 8. | Page 45

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.

Evaluation | Q V. 9. | Page 46

Suppose unknowingly you wrote the universal gravitational constant value as G = 6.67 × 1011. 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'?

Evaluation | Q V. 10. | Page 46

Calculate the gravitational field at point O due to three masses m1, m2 and m3 whose positions are given by the following figure. If the masses m1 and m2 are equal what is the change in a gravitational field at the point O?

Evaluation | Q V. 11. | Page 46

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 × 1024 kg and the mass of the Sun is 1.9 × 1030 kg.

Evaluation | Q V. 12. | Page 46

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.

Evaluation | Q V. 13. | Page 46

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?

Evaluation | Q V. 14. | Page 46

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?

Evaluation | Q V. 15. | Page 46

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?

Evaluation

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

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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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