If a gun is fired straight up into the air is the velocity of the bullet as it descends back to the ground powerful enough to kill or injure a human?

If a bullet is fired straight up, it will eventually slow down due to gravity and air resistance, stop at the top and then fall back to earth. As it falls, it accelerates until it reaches a constant speed known as terminal velocity. Terminal velocity is reached when the force of gravity is balanced by the air resistance opposing the movement of the projectile.

Studies, such as those conducted by the US Army, have shown that bullets fired into the air can reach terminal velocities of around 90 to 200 feet per second (27 to 61 metres per second), depending on the type of bullet. This speed is sufficient to penetrate the skin and cause serious injury.

There are numerous documented cases of people being injured or killed by bullets fired into the air. For example, celebratory gunfire often results in unintentional injury or death when the bullets come back down. Authorities and firearms safety experts consistently warn against firing guns into the air because of the risk of injury from falling bullets.

https://en.wikipedia.org/wiki/Celebratory_gunfire

https://www.cdc.gov/MMWR/preview/mmwrhtml/mm5350a2.htm