Two strings $A$ and $B$ produce beat of frequency $\Delta f_1>0$. The tension in string $A$ is slightly increased and the beat frequency is found to be $\Delta f_2>0$. If the original frequency of $A$ is $f_0$ and $\Delta f_2<\Delta f_1$, then the frequency of $B$ is

The distance between two successive minima of a transverse wave is 2.7 m . Five crests of the wave pass a given point along the direction of travel every 15.0 s . The speed of the wave is

Two waves of amplitudes $A_1$ and $A_2$ respectively, are superimposed. The ratio between the maximum and minimum intensities of the resultant waves is $9: 4$.

The value of $\frac{A_2}{A_1}$ is (assume $A_1>A_2$ )

Two trucks heading in opposite directions each with speed $0.1 u$, approach each other. The speed of the sound is $u$. The driver of first truck sounds his horn of frequency 495 Hz . Let $v_1$ and $v_2$ are the frequencies heard by the driver of second truck, when the trucks approach each other and when the trucks have passed each other. The magnitude of $v_1-v_2$ is