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7nadin3 [17]
3 years ago
8

An alert physics student stands beside the tracks as a train rolls slowly past. He notes that the frequency of the train whistle

is 496 Hz when the train is approaching him and 478 Hz when the train is receding from him. Using these frequencies, he calculates the speed of the train. What value does he find? (Assume the speed of sound in air is 343 m/s.)
Physics
1 answer:
Mnenie [13.5K]3 years ago
8 0

Answer:

6.455 m/s

Explanation:

Given;

Frequency of train whistle, f = 496 Hz

Frequency observed, f' = 478 Hz

Speed of sound in air = 343 m/s

Now,

From the instant Doppler's effect, we have the relation

f = \frac{v+v_s}{v-v_s}\times f'

here,

v is the speed of the sound

v_s is the speed of the train

496 = \frac{343+v_s}{343-v_s}\times478

or

1.037 × ( 343 - v_s ) = 343 + v_s

or

355.91 - v_s = 343 + v_s

or

12.91 = 2v_s

or

v_s  = 6.455 m/s

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