An engine is continuously emitting sound of frequency 1.2 kHz moving uniformly along a straight track. A stationary listener is situated off the track at a perpendicular distance of l = 350 m. The velocity of engine is equal to 50 m/s and the velocity of sound is 350 m/s. Find the frequency of sound received by the listener at the moment when the engine gets closest to him.

Explanation

To solve the problem of finding the frequency of sound received by the listener when the engine is closest to him, we can follow these steps:

### Step 1: Identify the Given Values
- Frequency of the sound emitted by the engine, \( f_s = 1.2 \, \text{kHz} = 1200 \, \text{Hz} \)
- Velocity of the engine (source of sound), \( v_s = 50 \, \text{m/s} \)
- Velocity of sound in air, \( v = 350 \, \text{m/s} \)
- Perpendicular distance from the track to the listener, \( l = 350 \, \text{m} \)

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