Solution: Let m and m be the masses of the bullet and the wood block respectively, the speed of the bullet entering the wood block is V, and the speed of moving together with the wood block is V. In the process of collision, the momentum of the bullet and the wood block system is conserved, then:

mv=(m+M)V ( 1)

For bullets, wood blocks, springs and the earth system, using the principle of kinetic energy, there are:

AE+Aid =δEk+δEp(2)

Where Ae=0, when the spring is compressed by X, the work done by friction is:

Aid=-μ(m+M)gx

Therefore, Formula (2) can be expressed as:

-μ(M+M)GX =[0- 1/2(M+M)V2]+

( 1/2kx2-0)

Substitute (1) into the above formula: v = 319.2m/s.