Explain why space junk is a hazard to an astronats or spacecraft

Space junk is travelling so fast that a collision with an astronaut or a spacecraft could be disastrous.

Explanation:

Space junk orbits the Earth at speeds of about 28 000 km/h.  

That's so fast that even an orbiting fleck of paint has enough kinetic energy to cause impact craters on the surface of a spacecraft. They are even more dangerous to an astronaut on a space walk.

Much of the space debris is larger and more dangerous than a fleck of paint.

One rough estimate of the amount of space debris is

      Size                Number of objects

< 1 cm                        200 000 000

1 cm to 10 cm                   700 000

> 10 cm                                 30 000

Satellites, etc.                       18 000

The chances of collision are small, but any collision can be disastrous.