A train whistling at constant frequency is moving towards a station at a constant speed $v$. The train goes past a stationary observer on the station. The frequency $n$ of the sound as heard by the observer is plotted as a function of time $t$. Identify the expected curve

$56$ tuning forks are so arranged in increasing order of frequencies in series that each fork gives $4$ beats per second with the previous one. The frequency of the last fork is the octave of the first. The frequency of the first fork is ..... $Hz$

A string of mass $2.5\, kg$ under some tension. The length of the stretched string is $20\, m$. If the transverse jerk produced at one end of the string takes $0.5\, s$ to reach the  other end, tension in the string is .... $N$

A man is watching two trains, one leaving and the other coming with equal speed of $4\,m/s$ . If they sound their whistles each of frequency $240\, Hz$ , the number of beats per sec heard by man will be equal to: (velocity of sound in air $= 320\, m/s$ )

A pulse on a string is shown in the figure. $P$ is particle of the string. Then state which of the following is incorrect

A plan wave of sound traveling in air is incident upon a plan surface of a liquid. The angle of incidence is $60^o$. The speed of sound in air is $300\ m/s$ and in the liquid it is $600\ m/s$. Assume Snell's law to be valid for sound waves