In a standing wave on a string.

Options

A. in one times period all the particle are simultaneously at rest once.
B. all the particles must be at their positive extremes simultaneously once in one times period
C. All the particles may be at their positive extremes simultaneously once in a time period.
D. All the particles are never at rest simultaneously.

Explanation

`y=2A sin kx.sin omegat`
`V_(y)=(dy)/(dt) =2A sinkx.cos omegat`
`V_(y)=0 rArr t=T//4 , 3T//4 (T=(2pi)/(omega))`
(2 times in one time period)