Suresh standing symmetrically between two cliffs claps his hands and starts hearing a series of echoes at intervals of 1 second. If speed of sound in air is 340 m/s, the distance between the parallel cliffs must be

Options

A. 320 m
B. 340 m
C. 680 m
D. 760 m

Explanation

To solve the problem, we need to determine the distance between the two cliffs based on the information provided.

### Step-by-Step Solution:

1. **Understanding the Setup**:
- Suresh is standing symmetrically between two cliffs.
- When he claps, the sound travels to each cliff and reflects back to him.

2. **Identifying the Echo Time**:
- Suresh hears the echo after 1 second. This means the total time taken for the sound to travel to one cliff and back is 1 second.

3. **Calculating the Distance Travelled by Sound**:
- The speed of sound in air is given as 340 m/s.
- In 1 second, the sound travels a total distance of:
\[ \text{Distance} = \text{Speed} \times \text{Time} = 340 \, \text{m/s} \times 1 \, \text{s} = 340 \, \text{m} \]

4. **Understanding the Journey of Sound**:
- The sound travels to one cliff and back, which means the distance to one cliff is half of the total distance travelled.
- Therefore, the distance to one cliff is:
\[ \text{Distance to one cliff} = \frac{340 \, \text{m}}{2} = 170 \, \text{m} \]

5. **Calculating the Total Distance Between the Cliffs**:
- Since Suresh is in the middle, the total distance \(D\) between the two cliffs is:
\[ D = 2 \times \text{Distance to one cliff} = 2 \times 170 \, \text{m} = 340 \, \text{m} \]

### Final Answer:
The distance between the parallel cliffs must be **340 meters**.

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