Class 9 Science - Chapter Sound NCERT Solutions | An echo returned in 3 s. What is the dis

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.

How is ultrasound used for cleaning?

Explain how the human ear works.

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

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?

A bus decreases its speed from 80 km h^-1 to 60 km h^-1 in 5 s. Find the acceleration of the bus.

Compare all the proposed models of an atom given in this chapter.

A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate
(i) the maximum height to which it rises,
(ii) the total time it takes to return to the surface of the earth.

An object of mass 100 kg is accelerated uniformly from a velocity of 5 m s^-1 to 8 m s^-1 in 6 s. Calculate the initial and final momentum of the object. Also, find the magnitude of the force exerted on the object.

Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?

When will you say a body is in

(i) uniform acceleration? (ii) non-uniform acceleration?

State which of the following situations are possible and give an example for each of these:

(a) an object with a constant acceleration but with zero velocity
(b) an object moving in a certain direction with an acceleration in the perpendicular direction.

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

What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.