A cord is used to lower vertically a block of mass M by a distance d with constant downward acceleration g4. Work done by the cord on the block is

When the block moves vertically downward with acceleration g4 then tension in the cordT=Mg−g4 =34MgWork done by the cord = F→.s→=Fscosθ=Tdcos(180°)=−3Mg4×d=−34Mgd