No, if a 9mm bullet were to travel at the speed of light, it would not go through the armor of a tank. While the speed of light is extremely fast, it does not change the fundamental properties of matter. In this hypothetical scenario, the bullet would still be composed of regular matter, and the tank's armor would also consist of conventional materials.
The ability of a bullet to penetrate armor depends on factors such as its mass, velocity, shape, and the properties of the armor itself. While increasing the velocity of a bullet can enhance its penetration capabilities, reaching the speed of light is not possible for objects with mass, according to our current understanding of physics.
Moreover, even if we ignore the practical impossibility of accelerating a bullet to the speed of light, other factors would come into play. At such extreme velocities, the bullet would likely experience relativistic effects, such as an increase in mass and a decrease in its interaction with matter. These effects would further complicate its ability to penetrate the armor.
In summary, while traveling at the speed of light is not feasible for a bullet, even if it were, it would not guarantee the ability to penetrate the armor of a tank.