Class 9 Science - Chapter Natural Resources NCERT Solutions | Why is the atmosphere essential for life

List any three human activities that you think would lead to air pollution.

What causes winds?

Why do organisms need water?

Why is water essential for life?

We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?

List any three human activities which would lead to an increase in the carbon dioxide content of air.

How does the atmosphere act as a blanket?

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

You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?

What is the greenhouse effect?

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?

State the universal law of gravitation.

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.

Who discovered cells, and how?

When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?

Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?

A bus starting from rest moves with a uniform acceleration of 0.1 m s^-2 for 2 minutes. Find (a) the speed acquired, (b) the distance travelled.

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?

Which wave property determines
(a) loudness,    (b) pitch?

A hammer of mass 500 g, moving at 50 m s^-1, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer?

What are the various energy transformations that occur when you are riding a bicycle?

Name the three sub-atomic particles of an atom.

Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s^-1. Calculate the initial recoil velocity of the rifle.