Q1Written answer
An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms-1?
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Worked solution
Speed of sound (v) = 342 ms-1
Echo returns in time (t) = 3 s
Distance travelled by sound = v × t = 342 × 3 = 1026 m
In the given interval of time, sound must travel a distance which is twice the distance between the reflecting surface and the source.
Therefore, the distance of the reflecting surface from the source =1026/2 = 513 m