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 .

Options

A. mg
B. `mg(1-h/d)`
C. `mg(1+h/d)`
D. `mg(1+h/d)^2`

Answer

C

Explanation

`v^2 =u^2 +2aS`
`implies 0 = (sqrt(2gh))^2 + 2(g-a)d`
`implies a = (1+h/d)g`
`F = mg (1+h/d)`