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 [BHU 2002]

• A.             \[mg\]  
• B.             \[mg\left( 1-\frac{h}{d} \right)\]
• C.             \[mg\left( 1+\frac{h}{d} \right)\]
• D.               \[mg{{\left( 1+\frac{h}{d} \right)}^{2}}\]