Question

Two tuning forks with natural frequencies of 340 Hz each move relative to a stationary observer. One fork moves away from the observer while the other moves towards him at the same speed. The observer hears beats of frequency 3 Hz. The speed of the tuning fork is (velocity of sound = 340 m/s)

• A. 1.5 m/s
• B. 0.45 m/s
• C. 3 m/s
• D. 4.5 m/s

Answer 1

The correct option is A

1.5 m/s

$f^{{}^{\prime }}=\left(\frac{V}{V-V_s}\right)f,f^{{}^{\prime }}=\left(\frac{V}{V+V_S}\right)f$

Beat frequency = $f^{{}^{\prime }}-f^{\prime \prime }$

Placing beat frequency as 3 Hz, velocity of sound as 340 m/s and natural frequency f as 340 Hz, we'll get the speed of tuning fork(V) as 1.5 m/s.