Explanation:
The given data is as follows.
Mass of bullet 1,
= 7 g = 
Mass of block of wood, M = 1.10 kg
Bullet penetrates to depth,
= 9.60 cm = 
Mass of bullet 2,
= 7 g = 
Velocity of bullet = v
Let us assume that depth of penetration of the bullet is
.
According to the law of conservation of energy,
Kinetic energy = Potential energy
Kinetic energy = 
and, Potential energy = mgh
so, for bullet 1
.......... (1)
For bullet 2,
Kinetic energy of bullet 1 - kinetic energy of bullet 2 = Potential energy

Using equation (1), we get


Putting the given values into the above formula as follows.

=
= 0.0953 m
or, = 9.53 cm (as 1 m = 100 cm)
Thus, we can conclude that the bullet will penetrate at a depth of 9.53 cm.