An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s-1?
Speed of sound, v = 342 m/s
Time taken by sound to travel from the source to reflecting surface, t = 3/2 = 1.5 s
Distance travelled by sound to reflecting surface from the source = v × t = 342 × 1.5 = 513 m
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?
Which wave property determines
(a) loudness, (b) pitch?
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 how the human ear works.
How is ultrasound used for cleaning?
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?
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Name A,B,C,D,E and F in the following diagram showing change in its state
What is the greenhouse effect?
Classify each of the following as a homogeneous or heterogeneous mixture.
soda water, wood, air, soil, vinegar, filtered tea.
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
Write a note on how forests influence the quality of our air, soil and water resources.
Name the regions in which parenchyma tissue is present.
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Explain how animals in Vertebrata are classified into further subgroups.
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?