Question 177: Waves

Question

A source of sound S is moving with a velocity of 50 m/s towards a stationary observer. The observer
measures the frequency of the source as 1000 Hz. What will be the apparent frequency of the source when it
is moving away from the observer after crossing him? (Take velocity of sound in air is 350 m/s)

Accepted Answer

$${f_a} = {V \over {V - {V_s}}}{f_o} = 1000\,Hz$$
$$f_a^{'} = {V \over {V + {V_s}}}{f_o}$$
$${{f_a^{'}} \over {{f_a}}} = {{V - {V_s}} \over {V + {V_s}}} = {{350 - 50} \over {350 + 50}} = {{300} \over {400}} = {3 \over 4}$$
$$f_a^{'} = {3 \over 4} 	imes 1000 = 750\,Hz$$

Answer

750 Hz

Answer

857 Hz

Answer

807 Hz

Answer

1143 Hz

Waves

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