A source of sound is moving with a velocity of 50 m s - 1 towards a stationary observer. The observer measures the frequency of sound as 500 H z . The apparent frequency of sound as heard by the observer when source is moving away from him with the same speed is (Speed of sound at room temperature is 350 m s - 1 )

Question

A source of sound is moving with a velocity of 50 m s - 1 towards a stationary observer. The observer measures the frequency of sound as 500 H z . The apparent frequency of sound as heard by the observer when source is moving away from him with the same speed is (Speed of sound at room temperature is 350 m s - 1 ), 400 Hz, 600 Hz, 375 Hz, 175.5 Hz

MARKS App · Accepted Answer

Speed of sound, v = 350 m s - 1 Velocity of sound, v = 50 m s - 1 From Doppler's principle, 1 s t case, f ′ = v v - v s f ......(i) 500 = 350 350 - 50 f Where, f = frequency of the source 2 n d case, f ' ' = v v + v s f f ' ' = 350 350 + 50 f ....(ii) From equation (i) and (ii) we get f ' ' 500 = 350 / 400 350 / 300 = 3 4 ∴ f ' ' = 500 × 3 4 = 375 Hz

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