Q: 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
(a) mg(1+h/d)
(b) mg(1+h/d)2
(c) mg(1-h/d)
(d) mg(1+d/h)
Ans: (a)
mg(h+d)= Fd