The equation of a stationary wave is $y=4sin\left(\frac{\mathrm{\pi }x}{5}\right)\mathrm{Co}s\left(100\mathrm{\pi t}\right)$ . The wave is formed using a string of length 20cm. The second and 3^rd antinodes are located at positions (in cm)

 Given

 The equation of stationary wave is

….(1)

General  stationary wave equation is

…..(2)

From equations (1)&(2),we have

A=4 , ,

k=propagation const=

Gap between antinodes is,

Second antinode position=

Third antinode position=