An open knife of mass m is dropped from a height h on a wooden floor. If the blade penetrates up to the depth d into the wood. The average resistance offered by the wood to the knife edge is to the depth d into the wood, the average resistance offered by the wood to the knife edge is .
A. mg(1+h/d)
B. mg(1+h/d)²
C. mg(1−h/d)
D. mg(1+h)
