question_answer

A man, standing between two cliffs, claps his hands and starts hearing a series of echoes at intervals of one second. If the speed of sound in air is 340 ms-1, the distance between the cliffs is                                   [KCET 2004]

A)            340 m                                      

B)            1620 m

C)            680 m                                      

D)            1700 m

Correct Answer: A

Solution :

            Total time taken for both the echoes \[t={{t}_{1}}+{{t}_{2}}=2\]sec but \[t=\frac{2{{d}_{1}}}{v}+\frac{2{{d}_{2}}}{v}\]\[\Rightarrow t=\frac{2}{v}\left( {{d}_{1}}+{{d}_{2}} \right)\]                    \[\Rightarrow ({{d}_{1}}+{{d}_{2}})=\frac{v\times t}{2}=\frac{340\times 2}{2}\]=340m.