Question

An echo repeats two syllables. If the velocity of sound is
330 m/s, then the distance of the reflecting surface is
(a) 66.0 m (b) 33.0 m
(c) 99.0 m (d) 16.5 m

Answer 1

Answer:

Let us say that we speak syllables at a rate of 2 to 9 per second. So let us say that a syllable takes a minimum of 0.1 sec for a fast speaker. Let us say that a sound pulse (syllable) is emitted starting at t = 0.

The effect of a syllable lasts on the ear for 0.1 sec. So if any echo reaches the year before t = 0.2 sec., then it is mixed with the direct sound present in the ear and so echo is not properly heard.

In this problem, two syllables are repeated in the echo. That is it took about 2 * 0.2 sec ie., 0.4 seconds for the sound to travel to the reflecting surface and come back to the ear.

The distance of the reflecting surface from the person

    = 330 m/s * 0.4 sec / 2

    = 66 meters

Explanation:

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