A sound wave of wavelength ` lambda` travels towards the right horizontally with a velocity `V`. It strikes and reflects from a vertical plane surface , travelling at a speed `v` towards the left . The number of positive crests striking in a time interval of `3 s` on the wall is

Options

A. `3(V+v)//lambda`
B. `3(V-v)//lambda`
C. `(V+v)//3lambda`
D. `(V-v)//3lambda`

Explanation

To solve the problem, we need to find the number of positive crests of a sound wave that strike a vertical wall in a time interval of 3 seconds. Here’s a step-by-step solution:

### Step 1: Understand the Relationship Between Wavelength, Velocity, and Frequency
The relationship between the speed of a wave (V), its wavelength (λ), and its frequency (f) is given by the equation:
\[ V = f \cdot \lambda \]
From this, we can express the frequency as:
\[ f = \frac{V}{\lambda} \]

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