Class 9 Science - Chapter Sound NCERT Solutions | Flash and thunder are produced simultane

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?

Why should preventive measures and biological control methods be preferred for protecting crops?

If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

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

Joseph jogs from one end A to the other end B of a straight 300 m road in 2 minutes 50 seconds and then turns around and jogs 100 m back to point C in another 1 minute. What are Joseph’s average speeds and velocities in jogging (a) from A to B and (b) from A to C?

During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, 3 × 10⁸ m s^-1.

Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

     (a) Atomic Nucleus      (b) Electron
     (c) Proton                     (d) Neutron

If the moon attracts the earth, why does the earth not move towards the moon?

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

Define 1 watt of power.

What are the different means by which infectious diseases are spread?