Standing stationary waves can be obtained in an air column even if the interfering waves are

$A$ $20 \ cm$ long string,having a mass of $1.0 \ g$,is fixed at both the ends. The tension in the string is $0.5 \ N$. The string is set into vibrations using an external vibrator of frequency $100 \ Hz$. Find the separation (in $cm$) between the successive nodes on the string.

In stationary waves,antinodes are the points where there is

$A$ string of length $0.5 \text{ m}$ and mass $10^{-3} \text{ kg}$ is tightly clamped at its ends. The tension in the string is $0.8 \text{ N}$. Identical wave pulses are produced at one end at equal intervals of time $\Delta t$. What is the minimum value of $\Delta t$ which allows constructive interference between successive pulses (in $\text{ s}$)?

Two sinusoidal waves with same wavelengths and amplitudes travel in opposite directions along a string with a speed $10 \, ms^{-1}$. If the minimum time interval between two instants when the string is flat is $0.5 \, s$,the wavelength of the waves is .... $m$

Which property distinguishes between progressive and stationary waves?