Class 9 Science - Chapter Natural Resources NCERT Solutions | Why do organisms need water?

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

What causes winds?

Why is the atmosphere essential for life?

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?

An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s?

Explain how the human ear works.

Explain how defects in a metal block can be detected using ultrasound.

A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.

Explain the working and application of a sonar.

How is ultrasound used for cleaning?

Explain how bats use ultrasound to catch a prey.

A freely falling object eventually stops on reaching the ground. What happenes to its kinetic energy?

What is loudness of sound? What factors does it depend on?

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?