Class 9 Science - Chapter Sound NCERT Solutions | Describe with the help of a diagram, how

Explain the working and application of a sonar.

Explain how sound is produced by your school bell.

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

Distinguish between loudness and intensity of sound.

A sound wave travels at a speed of 339 m s^-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?

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

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.

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

How is ultrasound used for cleaning?

Explain how the human ear works.

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?

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?

An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ¹⁶₈ X and ¹⁸₈ X in the sample?

When do we say that work is done?

An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?

Compare the use of manure and fertilizers in maintaining soil fertility.

A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.

Write an expression for the kinetic energy of an object.

A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.

What are the major divisions in the Plantae? What is the basis for these divisions?

Why does our palm feel cold when we put some acetone or petrol or perfume on it?