A bullet travelling at `200ms^(-1)` penetrates a wooden block of thickness 0.20 m and comes out at `20ms^(-1)`. Calculate the retardation produced inside the block. What additional thickness is required to stop the bullet.

Explanation

Given `v^(2)=v_(0)^(2)+2ax" "2a(0.20)=-[(200)^(2)-20^(2)]`
`a=(-220xx180)/(2xx0.2)`
`"i.e. "a=-110 xx900`
`a=-9.9xx10^(4)ms^(-2)`
Applying the same formula,
`0=200^(2)-19.8 xx10^(4)s`
`therefore" "x=(200xx200)/(19.8xx10^(4))=(40)/(198)=(20)/(99)" "x=0.2020 m`
`therefore" "Deltax =0.2020 m - 0.20 m = 0.002 m`