The diagram shows a string stretched between fixed points X and Y. There is a stationary wave on the string.
The solid curve shows the string at a position of maximum displacement at time 
. The dashed curve shows the other position of maximum displacement. The straight central dashed line shows the mean position of the string. Point S on the string is directly above point P. Point T on the string is directly below point Q. Which statement is correct?
A short time after , point R on the string will be displaced.
A short time after , points S and T on the string move in opposite directions.
The distance between P and Q is one wavelength.
Two moving points on the string that are equal distances from point R vibrate in phase.
