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Question
A man standing 48 m away from a wall fires a gun. Calculate the time after which an echo is heard. (The speed of sound in air is 320 ms-1).
Solution
Man's distance from the wall = 48 m
∴ 2d = for going and coming = 2 × 48 = 96 m
Speed of sound in air V = 320 ms-1
∴ Time after which echo is heard t = `(2d)/V`
t = `96/320`
= `3/10`
= 0.3 s
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