Option 1 : 340 m

__CONCEPT:__

**Echo**is the acoustical phenomena**in which there occurs a repetition of sound**which is caused**by the reflection of sound**waves from an obstacle is known as echo- For in order to occur echo the
**distance between the obstacle and sound source**must be**17.2 m**.

- For in order to occur echo the

__CALCULATION :__

Given - V = 340 ms^{-1}

Let x be the distance between the man and cliffs. If echo is occurs the sound has to travel the same distance twice,

- The
**total distance travelled by sound wave**is given by

⇒ X_{total} = 2X

- The velocity of the sound wave is given by

\(\Rightarrow V =\frac{X_{total}}{t}\)

Substituting the value of V and taking the value of t = 1sec

\(⇒340 =\frac{2x}{1}\)

\(⇒ x = 170 m\)

- The
**distance between the cliffs and the source**is**170 m**. - Then the distance between the two cliffs = 170 + 170 = 340 m. Hence,
**option 1 is the answer**