A boy standing at some distance from a cliff claps his hands and heard an echo $3s$ later. What is the distance of the cliff from the boy, if speed is $340 m{s}^{-1}$.

An echo involves the sound traveling from the source to the cliff and reflecting back, so the total distance traveled by the sound is twice the distance between the boy and the cliff. Using the distance formula, this total distance is 340 m/s multiplied by 3 s, which equals 1020 m. Dividing this total sound path by 2 gives the actual distance of the cliff from the boy as 510 m.

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