Class 9 Science - Chapter Sound NCERT Solutions | Two children are at opposite ends of an

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.

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?

Distinguish between loudness and intensity of sound.

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

How is ultrasound used for cleaning?

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

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?

List the points of differences between homogeneous and heterogeneous mixtures.

Define 1 watt of power.

Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Why are manure and fertilizers used in fields?

A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h^-1 in 10 minutes. Find its acceleration.

How does the force of gravitation between two objects change when the distance between them is reduced to half ?

How would you confirm that a colourless liquid given to you is pure water?

Identify the solutions among the following mixtures.

(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water.

Explain the following giving examples.

(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension

What is the role of epidermis in plants?