# NIOS Class 10 Science and Technology Chapter 11 Gravitation

NIOS Class 10 Science and Technology Chapter 11 Gravitation Solutions to each chapter is provided in the list so that you can easily browse through different chapters NIOS Class 10 Science and Technology Chapter 11 Gravitation and select need one. NIOS Class 10 Science and Technology Chapter 11 Gravitation Question Answers Download PDF. NIOS Study Material of Class 10 Science and Technology Notes Paper 212.

## NIOS Class 10 Science and Technology Chapter 11 Gravitation

Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 10 Science and Technology Chapter 11 Gravitation, NIOS Secondary Course Science and Technology Solutions for All Chapters, You can practice these here.

### Gravitation

Chapter: 11

INTEXT QUESTIONS 11.1

1. Why do two students sitting close to each other not feel force of gravitational attraction between them?

Ans: Gravitational force is extremely weak. Therefore, small masses do not attract each other due to this force.

2. Distance between two bodies is increased by a factor of four. How much will be the change in the force of gravitation?

Ans: As the force of gravitation is inversely proportional to the square of the distance between two bodies, the force will decrease by a factor of 1/16.

3. Why is G known as a universal gravitational constant?

Ans: The value of G is same everywhere on the earth or in the universe. Therefore, G is known as a universal gravitational constant.

INTEXT QUESTIONS 11.2

1. What do you mean by acceleration due to gravity?

Ans: The acceleration produced due to force of attraction by the earth is known as acceleration due to gravity.

2. Why do a heavier and a lighter object when dropped from a same height fall at the same rate?

Ans: Because the acceleration due to gravity is the same for both heavy and light objects.

3. State SI unit of acceleration due to gravity.

Ans: SI unit for acceleration due to gravity is ms–2.

4. Write equations of motion of an object moving under gravity.

Ans: Equations of motion

V = u + gt

S = ut + ½ gt2

V2 = u2 + 2 gs.

INTEXT QUESTIONS 11.3

1. Write two differences between mass of an object and its weight.

Ans: Mass is the quantity of matter contained in a body. Man of a body remains the same at all places. Weight of an object on earth is the force with which it is attracted towards the earth. Weight of an object changes from place to place.

2. State two factors on which weight of an object depends.

Ans: Weight of an object depends upon

(i) Mass of the body.

(ii) Acceleration due to gravity.

3. What will be the weight of an apple while it is falling from a tree?

Ans: Zero.

INTEXT QUESTIONS 11.4

1. Hold a mug full of water inside a bucket filled with water. Now lift it above the surface of the water. Why do you feel it is heavier now?

Ans: When immersed in water a buoyant force acts on the mug. Therefore, it feels lighter inside water.

When lifted above the surface of water it feels heavier.

2. Why does a piece of cork released under water bounce back?

Ans: Due to buoyant force (or upthrust).

3. What do you mean by buoyant force?

Ans: When an object is immersed in a fluid it experiences an upward force which is known as buoyant force.

4. Does the buoyant force act on a body when it is kept in vacuum?

Ans: No.

5. State two applications of Archimedes’ principle.

Ans: Two application of archimedes principle are mentioned below:

(i) In designing ships and submarines.

(ii) Hydrometers or lactometers.

1. State Newton’s law of gravitation.

Ans: Newton expressed the law of gravitation in the language of mathematics. He stated the law as follows:

Every particle in the universe attracts every other particle with a force. This force is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force is along the line joining the two particles. Mathematically,

where m1 and m2 are the masses of the two particles separated by a distance r.

2. How does the force of gravitation between two objects change when the distance between them is doubled?

Ans: When the distance between the objects is doubled then force between them is one fourth. When the distance between the objects is tripled then force between them is one ninth. When the masses of both objects are doubled then the force between them is four times.

3. How does the gravitational force between two objects change if the masses of both objects are doubled?

Ans: As, F = Gm1m2/r^2.

So, when masses are doubled then the force will be 4F.

4. Derive an expression for the acceleration due to gravity on the surface of the earth in terms of earth’s mass, gravitational constant and radius of earth.

Ans: Let masses of two objects is m1 and m2 and the distance between them is r.

So, according to Newton’s principle F~m1×m2 and F = 1/r^2.

Then, F=m1×m2/r^2.

Or, F = Gm 1×m2/ r^2. Where G is a universal gravitational constant.

5. Write the equations of motion of an object moving or falling only under gravity.

Ans: The equation of motion of an object moving or falling only under gravity is F = mg, where m = mass, g = acceleration due to gravity.

6. What are the differences between the mass of an object and its weight? On what factors does the weight of an object depend?

Ans: The mass of an object is the sum of masses of different particles present in it and the weight of any object is determined by the multiplication of the mass and the gravitational constant.

This weight is dependent on the gravitational acceleration and the height from the earth.

7. Why does a capped empty plastic bottle released under water bounce back to the surface of water?

Ans: As the density of plastic is less than that of water, the buoyant force is greater than its weight. This explains why the plastic block comes up to the surface of the water as soon as it is released under water.

8. What is force of buoyancy? What are the factors on which the magnitude of the buoyant force acting on a body at a given place depends?

Ans: The buoyant force is the upward force exerted on an object wholly or partly immersed in a fluid. This upward force is also called Upthrust. Due to the buoyant force, a body submerged partially or fully in a fluid appears to lose its weight, i.e. appears to be lighter.

9. State Archimedes’ principle. Give two applications of Archimedes’ principle.

Ans: The Archimedes principle states that if a body is immersed in a fluid, then the body experiences an upward force which is equal to the weight of the fluid displaced by it. This principal depends on

(i) density of the fluid.

(ii) volume of the body immersed in the fluid.

10. If the average distance between the earth and the sun is 1.5 × 1011 m, calculate the force of gravitation between the two. Given: mass of the earth = 6 ×1024 kg mass of the sun = 2 ×1030 kg value of G = 6.7 ×10–11 Nm2kg–2 .

Ans: The force of gravitation is, f = G×m1×m2/R^2.

Here, m1 = 6×10^24 kg and m2 = 2×10^30kg, G = 6.7×10^-11.R = 1.5×10^11m.

Then, f = 6.7×10^-11×6×10^24×2×10^30 / (1.5×10^11).

Or, f = 53.6×10^32 N.

11. What is the mass of an object whose weight is 49N? (Given g = 9.8 ms–2).

Ans: We know, F = ma;

Where m = mass=?

A = g = 9.8 m/s^2.

And F = force = 49N.

So, 49 = 9.8×m.

Or, m = 5kg.

12. A stone is dropped from the top of a tower 45 m high. What is its velocity when it hits the ground? (Given g = 10 ms–2).

Ans:  As, v^2 = u^2 + 2gh,

Where v = final velocity,

u = initial velocity = 0, g = 10.

So, v^2 = 0 + 2×10×45

Or, v = 30.

13. A body weighs 3.5 N in air and 2 N in water. How much buoyant force acts on the body?

Ans: The buoyant force= weight in air – weight tin water,

Or, The buoyant force = 3.5 – 2 = 1.5N.

14. A body is immersed in a liquid. If the liquid displaced by the body weighs 1 N then what is the buoyant force acting on the body?

Ans: We all know that the buoyancy force of an object is known as the amount of liquid displaced by upper thrust which is 1N.

Buoyant force= liquid displaced by 1N force.

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