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Category: Class 9

What is reverberation? How can it be reduced?

Class 9 Physics Sound
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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?

Class 9 Physics Sound
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A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 10 m s–2 and speed of sound = 340 m s–1 .

Class 9 Physics Sound
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Give two practical applications of reflection of sound waves.

Class 9 Physics Sound
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When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?

Class 9 Physics Sound
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Does sound follow the same laws of reflection as light does? Explain.

Class 9 Physics Sound
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The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

Class 9 Physics Sound
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Q25. What do you learn about the Kangaroo from the poem?

Class 9 English
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Q24. What do you learn about the Duck from the poem?

Class 9 English
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Q23. The Kangaroo does not want to catch ‘rheumatism’. Why is it spelt differently? Why is it in two parts? Why does the second part begin with a capital letter?

Class 9 English
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Q22. How did the Duck and the Kangaroo go round the world?

Class 9 English
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Q21. What did the Duck do to overcome the Kangaroo’s objection?

Class 9 English
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