A person rings a metallic bell near a strong concrete wall. He hears t

A person rings a metallic bell near a strong concrete wall. He hears the echo after 0.3 s. If the sound moves with a speed of 340 m/s, how far is the wall from him?

[amp_mcq option1=”102 m” option2=”11 m” option3=”51 m” option4=”30 m” correct=”option3″]

This question was previously asked in

UPSC CDS-1 – 2016

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The sound travels from the person to the wall and then reflects back to the person as an echo. The total distance covered by the sound is twice the distance between the person and the wall. The time taken for this round trip is 0.3 seconds, and the speed of sound is 340 m/s.
Total distance = Speed × Time
Total distance = 340 m/s × 0.3 s = 102 meters.
The distance to the wall is half of the total distance.
Distance to wall = Total distance / 2 = 102 m / 2 = 51 meters.

An echo involves sound travelling to a surface and back, so the distance to the surface is half the total distance covered by the sound.

The speed of sound in air is approximately 343 m/s at 20°C, but it varies with temperature and humidity. The value 340 m/s used in the problem is a typical approximation.

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