A train approachign a railway crossing at a speed of `120 kmh^-1` sounds a short whistle at frequency 640 Hz when it is 300 m away from the crossing. The speed of sound in air is `340 ms^-1`. What will be the frequency heard by a person standing on a road perpendicular to the track through the crossing at a distance of 400 m from the crossing ?

Explanation

To solve the problem, we will follow these steps:

### Step 1: Convert the speed of the train from km/h to m/s
The speed of the train is given as \(120 \, \text{km/h}\). To convert this to meters per second (m/s), we use the conversion factor:
\[ \text{Speed in m/s} = \frac{\text{Speed in km/h}}{3.6} \]
Calculating:
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