An open knife edge of mass 'm' is dropped from a height 'h' on a wooden
floor. If the blade penetrates upto the depth 'd' into the wood, the average resistance offered by the wood to the knife edge is
Let the blade stops at depth d into the wood.
v2=u2+2aS
⇒0=(√2gh)2+2(g−a)d
by solving a = (1+hd)g
So the resistance offered by the wood = mg(1+hd)