Copper has a FCC i.e. face centered cubic crystal structure. The 100 plane is essentially a planar section of the cubic cell where 4 Cu atoms occupy the 4 corners of the plane along with 1 Cu atom at the center of that plane. Each of the Cu atoms in the corners is shared by 4 adjacent unit cells. Thus, there are 2 Cu atoms present in the 100 plane (4*1/4 + 1 = 2).
Now, the planar density PD along the 100 plane is given as:
PD(100) = # atoms in the 100 plane/Area of 100 plane
= 
Here R = radius = 0.128 nm = 
PD = 
Answer:
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
<em> </em><u>Size</u><em> </em> <u>Number of objects</u>
< 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.
Solid liquid and gas is the answer
