Which of the following statements are true for wave motion?

A sound wave is passing through air column in the form of compression and rarefaction. In consecutive compressions and rarefactions,

Equation of a plane progressive wave is given by $y=0.6 \sin 2 \pi\left(t-\frac{x}{2}\right) .0$ n reflection from a denser medium its amplitude becomes $\frac{2}{3}$ of the amplitude of the incident wave. The equation of the reflected wave is

A string of mass 2.5 kg is under tension of 200 N . The length of the stretched string is 20.0 m . If the transverse jerk is struck at one end of the string, the disturbance will reach the other end in

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 $n^{\prime}$ of the sound as heard by the observer is plotted as a function of time $t$ (figure). Identify the expected curve.