It should be said right away that real asteroids do not have such high speeds and natural mechanisms are unknown to science that can accelerate an asteroid even up to 10% of the speed of light. Velocities comparable to the speed of light in space can acquire only individual particles.
A collision of an asteroid with the Earth's atmosphere at a near-light speed will be almost identical to an impact on the planet's surface. The outcome of such a collision will depend on the size, shape and composition of the asteroid, as well as on the angle at which it enters the atmosphere.If the impact is tangential and the asteroid only hits the upper layers of the atmosphere, then we will not even notice it, the trail from such a collision will be so weak and disappear so quickly that it can only be noticed with the help of special equipment. The reason for this is that the dimensions of the asteroid indicated in the question are too small, if it were the size of a soccer ball, the trail would be visible to the naked eye.But if such a small asteroid enters the dense layers of the atmosphere, the stratosphere, or even more so the troposphere, it will completely burn out there. The speed of combustion and the height to which the asteroid has time to fly depends on its shape, size and angle of incidence, but in any case, a huge amount of energy will be released during this combustion.To make the calculations, I took an asteroid's mass of 50 grams and used the kinetic energy formula, taking into account relativistic effects. As a result, it turned out that with the complete combustion of the asteroid in the atmosphere, an energy equivalent to the explosion of a 100-megaton nuclear bomb would be released. For comparison: a bomb with a capacity of 18 kilotons was dropped on Hiroshima, that is, 5555 times less; and the most powerful hydrogen bomb had the equivalent of only 58 megatons.The energy released during the combustion of the asteroid will not be concentrated in one point, as in the explosion of a bomb. Depending on the angle of incidence and how deep the asteroid penetrates into the atmosphere, it will be smeared over a huge space and, with luck, and the asteroid burns high in the stratosphere, damage to the planet's surface will be limited to broken windows in several countries. And if you are unlucky and the asteroid falls to the Earth strictly vertically, then the explosion may well raze the Moscow region to the ground, while knocking out windows in the entire European part of Russia. At the same time, regardless of the scenario, the explosion will be clean, that is, there will be no radioactive fallout and the damaged areas will be suitable for life.