A sharp knife of mass `m=1//2` kg penetrates `s=5`cm into fixed wooden block of mass `M=5` kg when it falls from a height of `h=2` m. How much will it penetrate when thrown horizontally with velocity `v = 10 m//s` ? How much will it penetrate if the block is free to move on smooth surface ?

Answer

`delta=(v^(2))/(2g(1+(h)/(s)))=12.44cm,delta'=(Mdelta)/(M+m)=22.39cm`