Class 9 Science - Chapter Gravitation NCERT Solutions | Why does a block of plastic released und

What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?

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

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

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

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

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

What is the acceleration of free fall?

The volume of a 500 g sealed packet is 350 cm³. 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?

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.

The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a force that is greater or smaller or the same as the force with which the moon attracts the earth? Why?

Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?

Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.

A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?

What is meant by a pure substance?

How does the sound produced by a vibrating object in a medium reach your ear?

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.

sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water

What are canal rays?

State any two conditions essential for good health.

How is our atmosphere different from the atmospheres on Venus and Mars?

Who discovered cells, and how?

How many atoms are present in a

(i) H₂S molecule and
(ii) PO₄^3- ion?

Are the answers to the above questions necessarily the same or different? Why?

Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?

What is the primary characteristic on which the first division of organisms is made?

Why do we classify organisms?

Where do the lipids and proteins constituting the cell membrane get synthesised?

Convert into mole.

(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.

If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Which do you think is a more basic characteristic for classifying organisms?

(a) the place where they live.
(b) the kind of cells they are made of. Why?

In which kingdom will you place an organism which is single-celled, eukaryotic and photosynthetic?