Question 98: Waves

Question

The frequency of echo will be __________ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h towards a hill from which an echo is heard by the train driver. Velocity of sound in air is 330 m/s.

Accepted Answer

$${v_s} = 36 	imes {5 \over {18}} = 10$$ m/sec
$$f = {{v + {v_s}} \over {v - {v_s}}}{f_0}$$
$$ = {{340} \over {320}} 	imes 320$$
$$ = 340$$ Hz

Waves

The frequency of echo will be __________ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h towards a hill from which an echo is heard by the train driver. Velocity of sound in air is 330 m/s.

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