A locomotive approaching a crossing at a speed of 80 mi/h sounds a whistle of frequency 400 Hz when 1 mi from the crossing. There is no wind, and the speed of sound in air is 0.200mi/s. What frequency is heard by an observer 0.60 mi from the crossing on the straight road which crosses the railroad at right angles?

Explanation

To solve the problem, we need to determine the frequency of the whistle heard by an observer located at a distance from the crossing, while the locomotive is moving towards the crossing. We will use the Doppler effect formula for sound waves.

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Speed of the locomotive (source), \( V_s = 80 \) mi/h
- Frequency of the whistle (source frequency), \( f_0 = 400 \) Hz
- Distance from the locomotive to the crossing, \( d_s = 1 \) mi
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