Please help me with this question:

Dear Student,
Energy of the bullet while hitting the wooden block is
$E=\frac{1}{2}m{v}^2=\frac{1}{2}\times 10\times {10}^{-3}\times 100=0.5 J$
This energy is used to do the work (W) in penetrating the wood
$$\begin{gathered} W=F.d=Fd \\ where, \\ F=average force exerted by the bullet on the block \\ d=10 cm=0.1 m \\ So, \\ F\times 0.1=0.5 \\ F=\frac{0.5}{0.1}=5 N \end{gathered}$$

Regards