Four different independent waves are represented by $(i)$ $y_1 = a_1 \sin \omega t$,$(ii)$ $y_2 = a_2 \sin 2\omega t$,$(iii)$ $y_3 = a_3 \cos \omega t$,and $(iv)$ $y_4 = a_4 \sin (\omega t + \frac{\pi}{3})$. With which two waves is interference possible?

$A$ pipe open at one end has a length of $0.8 \text{ m}$. At the open end of the tube, a string $0.5 \text{ m}$ long is vibrating in its first overtone and resonates with the fundamental frequency of the pipe. If the tension in the string is $50 \text{ N}$, what is the mass of the string (in $\text{ g}$)? (Neglect end correction, Speed of sound = $320 \text{ m/s}$)

$A$ massless rod of length $L$ is suspended by two identical strings $AB$ and $CD$ of equal length. $A$ block of mass $m$ is suspended from point $O$ such that $BO$ is equal to $x$. Further,it is observed that the frequency of the $1^{st}$ harmonic in $AB$ is equal to the $2^{nd}$ harmonic frequency in $CD$. The value of $x$ is

Which of the following statements is incorrect?

$A$ clamped string is oscillating in the $n^{th}$ harmonic,then

At a certain moment, the photograph of a string on which a harmonic wave is travelling to the right is shown. Then, which of the following is true regarding the velocities of the points $P$, $Q$ and $R$ on the string?