NCERT Solution (Class 11) > Physics Chapter 8 Gravitation

NCERT Solution (Class 11) > Physics Chapter 8 Gravitation

NCERT Solution Class 11 Physics Chapter 8 Gravitation: National Council of Educational Research and Training Class 11 Physics Chapter 8 Solution – Gravitation. Free PDF Download facility available at our website.

Board

NCERT
Class

11

Subject

Physics
Chapter

8

Chapter Name

Gravitation
Topic

Exercise Solution

Gravitation Chapter all Questions and Numericals Solution

 

Chapter 8- Gravitation

8.1) Answer the following:

(a) You can shield a charge from electrical forces by putting it inside a hollow conductor. Can you shield a body from the gravitational influence of nearby matter by putting it inside a hollow sphere or by some other means?

(b) An astronaut inside a small space ship orbiting around the earth cannot detect gravity. If the space station orbiting around the earth has a large size, can he hope to detect gravity?

(c) If you compare the gravitational force on the earth due to the sun to that due to the moon, you would find that the Sun’s pull is greater than the moon’s pull. (you can check this yourself using the data available in the succeeding exercises). However, the tidal effect of the moon’s pull is greater than the tidal effect of sun. Why?

ANSWER-

(a) Electric forces depend upon nature of the medium in which charge is placed. Gravitational force is independent of the nature of the material medium hence a body can’t be shielded from the gravitational influence of nearby matter.

(b) If the size of the space station is large then its gravitational effect can be measured and then the astronaut can detect gravity.

(c) Gravitational force depends inversely on the square of the distance on the other hand Tidal effect depends inversely upon the cube of the distance. Since the distance between the Moon and the Earth is smaller than the distance between the Sun and the Earth, the tidal effect of the Moon’s pull is greater than the tidal effect of the Sun.

 

8.2) Choose the correct alternative:

(a) Acceleration due to gravity increases/decreases with increasing altitude. (b) Acceleration due to gravity increases/decreases with increasing depth (assume the earth to be a sphere of uniform density). (c) Acceleration due to gravity is independent of mass of the earth/mass of the body. (d) The formula –GM m(1/r2– 1/r1) is more/less accurate than the formula mg(r2 – r1) for the difference of potential energy between two points r2 and r1 distance away from the centre of the earth.

Answer-

(a) Acceleration due to gravity at height h is given by

gh/g = (1-2h/R)

Where,

R = Radius of the Earth

g = Acceleration due to gravity on the surface of the Earth

gh = Acceleration due to gravity at height h

from above formula we can say that  that acceleration due to gravity decreases with an increase in height.

(b)Acceleration due to gravity at depth d is given by

gd/g = (1- d/r)

Acceleration due to gravity decreases with an increase in depth d.

 

(c) acceleration due to gravity is given by

G = gm/R2

Where,

G = Universal gravitational constant

M = Mass of the Earth

R = Radius of the Earth Hence,

Above formula does not contain the mass of body hence we conclude that acceleration due to gravity is independent of the mass of the body.

 

8.3) Suppose there existed a planet that went around the Sun twice as fast as the earth. What would be its orbital size as compared to that of the earth?

ANSWER-

Using keeper’s third law

 

8.4)

 

8.6) Choose the correct alternative:

(a) If the zero of potential energy is at infinity, the total energy of an orbiting satellite is negative of its kinetic/potential energy.

(b) The energy required to launch an orbiting satellite out of earth’s gravitational influence is more/less than the energy required to project a stationary object at the same height (as the satellite) out of earth’s influence.

ANSWER-

(a)Total energy of a satellite is the sum of its kinetic energy and  gravitational potential energy. At infinity, the gravitational potential energy of the satellite is then total energy is equal to kinetic energy. Total energy is considered as negative which shows that satellite is bound to earth.

(b)An orbiting satellite has some energy . This energy is due to  its orbital motion. It requires relatively lesser energy to move out of the influence of the Earth’s gravitational field than a stationary object on the Earth’s surface that initially contains no energy.

 

8.7) Does the escape speed of a body from the earth depend on (a) the mass of the body, (b) the location from where it is projected, (c) the direction of projection, (d) the height of the location from where the body is launched?

ANSWER-

Escape velocity of a body from the Earth is given by ,

Ve = √2gR

WHERE,

Ve = escape velocity

g = acceleration due to gravity

R = radius of earth

From above equation we can conclude that escape velocity Ve independent of the mass of the body and the direction of its projection along with location from where it is projected but it depends upon height from where body is launched.

 

8.8) A comet orbits the sun in a highly elliptical orbit. Does the comet have a constant (a) linear speed, (b) angular speed, (c) angular momentum, (d) kinetic energy, (e) potential energy, (f) total energy throughout its orbit? Neglect any mass loss of the comet when it comes very close to the Sun.

ANSWER-

Angular momentum and total energy are constant quantities while all other are changing from point to point.

 

8.9) Which of the following symptoms is likely to afflict an astronaut in space (a) swollen feet, (b) swollen face, (c) headache, (d) orientation problem?

ANSWER-

(a) Legs hold the entire mass of a body is hold by legs in standing position due to gravitational force but due to absence of gravity in space astronaut feels weightlessness. Therefore, swollen feet of an astronaut do not affect him in space.

(b) Due to weightlessness in eyes, ears, nose, and mouth face gets swallow. This symptom can affect an astronaut in space because it directly affect the speaking and watching ability of person.

(c) Headaches can affect the working of an astronaut in space.

(d) orientation problem can affect an astronaut in space.

 

8.10) In the following two exercises, choose the correct answer from among the given ones: The gravitational intensity at the centre of a hemispherical shell of uniform mass density has the direction indicated by the arrow (see Fig 8.12) (i) a, (ii) b, (iii) c, (iv) 0

ANSWER- iii

Gravitational intensity is given by,

I = -dV/dr

Where V is Gravitational potential.

Gravitational potential (V) is constant at all points in a spherical shell. Hence, the derivative of gravitational potential is zero inside the spherical shell. Hence Gravitational intensity is also zero at all points inside the spherical shell from above formula. Hence gravitational force is symmetrical everywhere but If the upper half of a spherical shell is cut out then the net gravitational force acting at centre O will be in the downward direction as upward force is not present.

 

8.11) For the above problem, the direction of the gravitational intensity at an arbitrary point P is indicated by the arrow (i) d, (ii) e, (iii) f, (iv)g.

ANSWER- ii

Gravitational intensity is given by,

I = -dV/dr

Where V is Gravitational potential.

Gravitational potential (V) is constant at all points in a spherical shell. Hence, the derivative of gravitational potential is zero inside the spherical shell. Hence Gravitational intensity is also zero at all points inside the spherical shell. Hence gravitational force is symmetrical at all points.

At point p net force will be in downward direction as upper part is cut off hence gravitational intensity is also in downward direction along direction of e.

 

8.12) 

 

8.15)

 

In case you are missed :- NCERT Solution for Motion In A Plane

 

8.16) 

 

8.21)

 

8.23) 

 

8.24) 

 

8.25) 

In case you are missed :- NCERT Solution for Laws of Motion

Updated: April 17, 2023 — 11:34 am

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