solution: dF P=0·n dw=dF. ds mIc dmac =(d)Pb P- total stress on plane element dw mac P.×dsb=(0,)×dsb dl×ds d/xds(a·b) dl×ds =(·b)·(dl×ds) (a·b)×dldl F f d d   = P n   =  W F s   d mic = d d W A P b   d mac = (d )  W P l S b n l S b          d mac =  d d  = (  ) d d  l s l s l s b        d d d d d d ( )   =     ( b) (dl ds)    =     b l s    = (  )d d P － total stress on plane element  solution: