An open knife edge of mass 200 g is dropped from height 5m on a cardboard. If the knife edge penetrates a distance 2m into the card board, the average resistance offered by the cardboard to the knife edge is $(g = 10 {ms}^{- 1})$

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25N

35N

100N

answer is A.

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Detailed Solution

We can use work energy theorem, Total kinetic energy lost is K = mg(h+d)
Work done by the resistance force F is W = Fd
By equating , We get $F = \frac{m g (h + d)}{d}$
$F = \frac{0.2 \times 10 (2 + 5)}{2} = 7 N$
Therefore the correct answer is A

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