I solved the problem with a reply from another tread.
from settings i choosed to use the side swithch for to lock/unlock rotation of the screen.
and when i was doing that the swith was in mute mode. so i keeps it muted and i didnt know that this was the problem. Now i set it back to sound setting mode and unmute the switch. everything works fine.
I guess apple should put another switch to control this under settings/general/side switch.
otherwise its so hard and confusing to figure that out while some apps have sound and some does not.