A source of sound of frequency `1000 H_(Z)` moves unifornly along a straight line with velocity `0.8` times velocity of sound . An observer is located at a distance `l= 250 m` from this line. Find
(a) the frequency of the sound at instant when the source is closest to the observer.
(b) the distance of the source when he observer no change in the frequency.

Explanation

To solve the problem step by step, we will break it down into two parts as per the question.

### Part (a): Finding the frequency of the sound when the source is closest to the observer.

1. **Understanding the scenario**:
- The source of sound has a frequency \( f_0 = 1000 \, \text{Hz} \).
- The source moves with a velocity \( v_s = 0.8 v \) where \( v \) is the speed of sound.
- The observer is at a distance \( l = 250 \, \text{m} \) from the line along which the source moves.
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