#### Chapters

Chapter 2 - Is Matter around us Pure

Chapter 3 - Atoms and Molecules

Chapter 4 - Structure of the Atom

Chapter 5 - The Fundamental Unit of Life

Chapter 6 - Tissues

Chapter 7 - Diversity in Living Organisms

Chapter 8 - Motion

Chapter 9 - Force and Laws of Motion

Chapter 10 - Gravitation

Chapter 11 - Work and Energy

Chapter 12 - Sound

Chapter 13 - Why do we fall Ill

Chapter 14 - Natural Resources

Chapter 15 - Improvement in Food Resources

## Chapter 10 - Gravitation

#### Page 136

What do you mean by free fall?

What do you mean by acceleration due to gravity?

#### Page 138

What are the differences between the mass of an object and its weight?

Why is the weight of an object on the moon 1/6^{th} its weight on the earth?

#### Page 141

Why is it difficult to hold a school bag having a strap made of a thin and strong string?

What do you mean by buoyancy

Why does an object float or sink when placed on the surface of water?

#### Page 142

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighingmachine. In reality, one is heavier than other. Can you say which one is heavier and why?

#### Pages 143 - 144

Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?

What is the importance of universal law of gravitation?

What is the acceleration of free fall?

What do we call the gravitational force between the Earth and an object?

Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same when he meets him at the equator. Will the friend agree with the weight of gold bought? If not, why? [*Hint*: The value of *g* is greater at the poles than at the equator].

Why will a sheet of paper fall slower than one that is crumpled into a ball?

Gravitational force on the surface of the moon is only `1/6` as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth?

A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate

(i) the maximum height to which it rises.

(ii)the total time it takes to return to the surface of the earth.

A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.

A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s^{2}, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?

A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.

In what direction does the buoyant force on an object immersed in a liquid act?

Why does a block of plastic released under water come up to the surface of water?

The volume of 50 g of a substance is 20 cm^{3}. If the density of water is 1 g cm^{−3}, will the substance float or sink?

The volume of a 500 g sealed packet is 350 cm^{3}. Will the packet float or sink in water if the density of water is 1 g cm^{−3}? What will be the mass of the water displaced by this packet?

#### Extra questions

A ball thrown up vertically returns to the thrower after 6 s. Find

(a) the velocity with which it was thrown up,

(b) the maximum height it reaches, and

(c) its position after 4 s.