“Human beings are strong because we have the ability to change ourselves.” Saitama, One Punch Man
The idea of stopping a meteor headed towards our planet with nothing but a superpowered human being sounds like a physical impossibility. But if you had a powerful enough, strong enough, fast enough human, it could be done, so long as you obeyed the laws of physics and conserved energy and momentum.
A map of the asteroid population by size. There are approximately a few million potential “10”s on the Torino scale, over 50 million potential “9”s and nearly a billion estimated potential “8”s. Image credit: Marco Colombo, DensityDesign Research Lab, under a c.c.a.-s.a.-4.0 license.
The speed your human would need to hit the meteor with would be tremendous; there would need to be something special about this human’s atoms to keep them from flying apart; the energy released by the in-air explosion would be catastrophically huge. But it could, in fact, save the city — or the entire planet — that it would have completely annihilated otherwise.