Answer
An internal energy of $4900~J$ is generated.
Work Step by Step
The increase in internal energy is equal to the initial kinetic energy of the bullet:
$\Delta E = \frac{1}{2}mv^2$
$\Delta E = \frac{1}{2}(0.020~kg)(7.00\times 10^2~m/s)^2$
$\Delta E = 4900~J$
An internal energy of $4900~J$ is generated.
