A train is moving towards a stationary observer. Which of the following curve best represents the frequency received by observer $f$ as a function of time ?

Three waves of equal frequency having amplitudes $10\,\mu m$, $4\,\mu m$, $7\,\mu m$ arrive at a given point with successive phase difference of $\pi /2$, the amplitude the resulting wave in $\mu m$ is given by

A string of mass $m$ and length $l$ hangs from ceiling as shown in the figure. Wave in string moves upward. $v_A$ and $v_B$ are the speeds of wave at $A$ and $B$ respectively. Then $v_B$ is

In a sinusoidal wave, the time required for a particular point to move from maximum displacement to zero displacement is $0.170 \,s$. The frequency of wave is ........ $Hz$

Two vibrating strings of the same material but lengths $L$ and $2L$ have radii $2r$ and $r$ respectively. They are stretched under the same tension . Both the strings vibrate in their fundamental modes, the one of length $L$ with frequency $f_1$ and the other with frequency $f_2$. The ratio $\frac{f_1}{f_2}$ is given by

The amplitude of a wave disturbance propagating in the positive $X-$ direction is given by $y = 1/(1 + x^2)$ at time $t = 0$ and by $y = 1/[1 + (x -1)^2]$ at $t = 2$ seconds, where $x$ and $y$ are in metres. The shape of the wave disturbance does not change during the propagation. The velocity of the wave is ..... $ms^{-1}$