1.

An open knife edge of mass M is dropped from a height h on a wooden floor. If the blade penetrates adistances into the wood, the average resistance offered by the wood to the blade is :-

Answer»

Mg
`Mg(1+h/s)`
`Mg(1-h/s)`
`Mg(1+h/s)^2`

Solution :Suppose F be the resistive force of WOODEN plank. It should oppose the weight of the body. Resultant force oppositeto the motion =F - Mg
Work done =(F-Mg) s=kinetic ENERGY
Velocity of FALL = `sqrt(2gh)`
`therefore (F-mg)s =1/2 M(sqrt(2gh))^2`
or `(F-Mg)s=1/2 M XX 2gh`
or `F=(Mgh)/s + Mg =Mg(1+h/s)`


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