[" 27.In Fig."7.278" ,the blocks are at rest and a force of "10N],[" acts on the block of "4kg" mass.The coefficient of static "],[" friction and the coefficient of kinetic friction are "mu_(s)=0.2],[" and "mu_(k)=0.15" for both the surfaces "],[" in contact.The magnitude of "],[" surface of contact between the "],[" surface of contact between the "2],[" kg and "4kg" block in this situation "],[[" a."3N," b."4N," c."3.33N," d.Zero "]]