• # question_answer An observer, situated between two parallel cliffs, emits an intense sound note. Two successive echoes are then heard after 5s and 7s. Calculate the distance between the cliffs. (Velocity of sound = $340\text{ }rn{{s}^{-1}})$

Let${{x}_{1}}$and${{x}_{2}}$be the distances of the two cliffs from the man. Then, $2{{x}_{1}}=340\times 5$ $=1700m$ $\Rightarrow$${{x}_{1}}=850m$ and $2{{x}_{2}}=340\times 7$ $=2380m$ $\Rightarrow$ ${{x}_{2}}=1190m$ $\therefore$distance between the two cliffs$={{x}_{1}}+{{x}_{2}}$ $=850+1190=2040m$