Question

The speed of sound in air at a given temperature is 350 m/s. An engine blows whistle at a frequency of 1200 cps. It is approaching the observer with velocity 50 m/s. The apparent frequency in cps heard by the observer will be

• A. 600
• B. 1050
• C. 1400
• D. 2400

Answer 1

Answer: (C)

1400

Answer 2

$n' = n\left( \frac{v}{v - v_{s}} \right) = 1200 \times \left( \frac{350}{350 - 50} \right)$=1400 cps