Sunil is standing betweenthe two walls . The wall closest to him is at a distance of 360 m If he shouts, he hear the first echo after 4 S and another after another 2 S ( 1 ) ( what is the velocity of sound in air ) ( 2 ) ( What is the distance betweenthe two walls )
Answers
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The first echo will be from the wall closest to Sunil, so the sound had to travel from Sunil to the wall to Sunil back again. The total distance travelled by sound will be 360 + 360 = 720 m
Time taken by sound is 4 s.
v of sound = 720/4
= 180 m/s
The second echo came at 4+2 = 6 s
Let distance from the second wall be d.
Then the distance travelled by sound from the second wall will be 2d.
180 = 2d/6
180 = d/3
d = 540 m
The distance between the two walls will be the sum of distance of Sunil from the first wall and distance of Sunil from the second wall
= 360 + 540
= 900 m
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Correct question:
- Sunil is standing between two walls the wall closest to him is at a distance of 660m if he shouts he hears the first echo after 4s and another after another 2 seconds.
Find
i) Velocity of sound in Air ?
ii) Distance between two walls
(As this question is from State board; And, It by printing mistake in some books, The distance is given as 360 meters; And answer is also given there as 330 and 1650 respectively; So, if we solve this problem by considering distance 360 meters, then answer will get wrong).
Answer:
Velocity = 330m/s
Distance between two walls = 1650 meters
Given information:
Suppose sunil is standing is a room between 2 walls.
Wall closest to sunil is at distance of 660 meters.
And, If he shouts, then he heard the Echo from his nearest wall in 4 seconds.
And, Another wall echo is heard in next 2 seconds.
To find: i) Velocity of sound in Air ?
ii) Distance between two walls
Explanation:
Method I :
i) Velocity of sound in Air:
Velocity = Distance / Time/2 (Because we heard sound after getting reflected back)
Velocity = 660 / 2
Velocity = 330 m/s
Therefore, Velocity of sound in Air is 330 m/s.
ii) What is the distance between two walls ?
For first wall,
Distance = ?
Velocity = 330 m/s
Time = 4 seconds
Distance = Velocity * time
Distance = 330 * 4
Distance = 1320 meters -------- (i)
For second wall,
Distance = ?
Time = 2 seconds
Velocity = 330 m/s
Distance = Velocity * 2/ time
Distance = 330 * 1
Distance = 330 meters ------- (ii)
Adding equation (i) and (ii),
Distance between 1st wall + Distance between 2nd wall = Distance between two walls
Distance between two walls = 1320 + 330
Distance between two walls = 1650 meters
Therefore, Distance between 2 walls is 1650 meters.
Method II :
i) Velocity of sound:
Velocity of sound = Distance/time
Velocity of sound = 660/2
Velocity of sound = 330 m/s
ii) Distance between two walls:
Distance = Velocity * total time
Distance = 330 * 6
Distance = 1650 meters