Question

A whistle giving out \(400\) Hz approaches a stationary observer at a speed of \(34\) m/s. The frequency heard by the observer (in Hz) is nearly (speed of sound\(=340\) m/s)

• A. \(400\)
• B. \(500\)
• C. \(444\)
• D. \(555\)

Hint:

For a source moving toward a stationary observer, use f' = f v/(v - vs).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Source approaches a stationary observer, so the apparent frequency increases:
\(f'=f\dfrac{v}{v-v_s}\)

Step 2: Substitution
\(f'=400\times\dfrac{340}{340-34}\)
\(=400\times\dfrac{340}{306}\)

Step 3: Calculation
\(f'=400\times1.111\approx444\) Hz

Final Answer:
The observer hears about 444 hertz. \[ \boxed{\text{(C) }444} \]