An open knife edge of mass M is dropped from a height I on a wooden floor. If the blade penetrates S into the wood, the average resistance offered by the wood tothe blade is

Let F be the resistive force of wooden plank. It should oppose the weight of the body.Resultant force opposite to the motion = F - M g,Work done = (F - M g)S = Kinetic energyVelocity of fall =(2gh)∴ (F−Mg)S=12M(2hg)2 or F=MghS+Mg=Mg1+hS.