The displacement of the medium in a sound wave is given by the equation:
$y_1=A\cos (ax+bt)$  where A, a & b are positive constant. The wave is reflected by an obstacle situated at x=0. The intensity of the reflected wave is 0.64 times that of the incident wave
 

The wavelength of the incident wave is $(2\pi /a)$ and its frequency is $(b/2\pi )$  
 

The equation for the reflected wave is $y_2=\pm 0.8A(ax+bt)$  
 

In the resultant wave formed after reflection, the maximum particle speed in the medium is (1.8 bA)

In the resultant wave formed after reflection, the minimum particle speed in the medium is zero