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 ?

The equation of a stationary wave is $Y = 10\,\sin \,\frac{{\pi x}}{4}\,\cos \,20\,\pi t$. The distance between two consecutive nodes in metres is

The phase difference between two points separated by $0.8 m$ in a wave of frequency $120 Hz$ is ${90^o}$. Then the velocity of wave will be ............ $\mathrm{m/s}$

A train is moving towards a stationary observer (at $t = 0$) with constant velocity of $20\ m/s$ and after sometime it crosses the observer. Which of the following curve best represents the frequency received by observer $f$ as a function of time ?

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 ?

If $n_1 , n_2$ and $n_3$ are the fundamental frequencies of three segments into which a string is divided, then the original fundamental frequency $n$ of the string is given by